The ancient Hellenes adored music, and it was a huge part of their religious devotion. Hymns were sung, and processions often accompanied with easy to carry instruments, adding to a festive mood and serving as a way to draw the attention of the Gods. Of course, the acient Hellenes carried different instruments than we are used to today, and I would like to make a short summary of the most common ancient Hellenic instruments--with lots of help from Wikipedia.

Aulos (αὐλός)
An aulos was an ancient Greek wind instrument, depicted often in art and also attested by archaeology. the player was called an 'aulete' (αὺλητής, aulētēs). There were several kinds of aulos. A single pipe without a reed was called the monaulos (μόναυλος), a single pipe held horizontally was the plagiaulos (πλαγίαυλος), and the most common variety was a double-piped reed instrument like an oboe (see below).The aulos was described as 'penetrating, insisting and exciting'. It's closest modern equivalent would be the clarinet.

Barbiton (βάρβιτον)
The barbiton, or barbitos (βάρβιτος) was an ancient stringed instrument related to the lyre. It was a bass version of the kithara, and belonged in the zither family. Although in use in Asia Minor, Italy, Sicily, and Greece, it is evident that the barbiton never won for itself a place in the affections of the Greeks of Hellas; it was regarded as a barbarian instrument affected by those only whose tastes in matters of art were unorthodox. It had fallen into disuse in the days of Aristotle, but reappeared under the Romans. Aristotle said that this string instrument was not for educational purposes but for pleasure only. It had a low pitch, and its closest modern equivalent would be the lyre, or perhaps the guitar.

Chelys (χέλυς)
The chelys (Greek: χέλυς, Latin: testudo), was a stringed musical instrument, the common lyre of the ancient Greeks, which had a convex back of tortoiseshell or of wood shaped like the shell. The word chelys was used in allusion to the oldest lyre of the Greeks, which was said to have been invented by Hermes, most notably in the Homeric Hymn to Him. Lyre's are still available today, so that would be the modern equivalent.

An epigonion was an ancient stringed instrument. It was invented, or at least introduced into Hellas, by Epigonus of Ambracia, a Hellenic musician of Ambracia in Epirus, who was admitted to citizenship at Sicyon as a recognition of his great musical ability and of his having been the first to pluck the strings with his fingers, instead of using the plectrum. The instrument, which Epigonus named after himself, had forty strings and most likely looked like a variation of the harp. It's likely it also sounded that way. Needless to say, the closes modern equivalent would be the harp itself.

Hydraulis (ὕδραυλις)
The hydraulis, or water organ, was a type of pipe organ blown by air, where the power source pushing the air is derived by water from a natural source or by a manual pump. Consequently, the water organ lacks a bellows, blower, or compressor. It is attributed to the Hellenistic scientist Ktesibios of Alexandria, an engineer of the 3rd century BC.  The hydraulis was the world's first keyboard instrument and was the predecessor of the modern (church) organ.

Kithara (κιθάρα)
The kithara was an ancient Hellenic musical instrument in the lyre or lyra family. It was a professional version of the folkish two-stringed lyre. Musicians who played the kitara were called 'kitharodes'. The kithara's origins are likely Asiatic. The barbiton was a bass version of the kithara. In modern Greek the word kithara has come to mean 'guitar', making that the closest modern equivalent, although the sounds would be quite different.

A krotlon (better known as 'crotalum') was a kind of clapper or castanet used in religious dances by groups in ancient Hellas, including the Korybantes, armed and crested dancers who worshipped the Phrygian goddess Kybele with drumming and dancing. It was made of shell and brass, as well as wood, and its modern equivalent is obviously the castanet.

Lyre (λύρα)
The lyre is a string instrument which was ordinarily played by being strummed with a plectrum, like a guitar or a zither, rather than being plucked, like a harp. The fingers of the free hand silenced the unwanted strings in the chord. The recitations of the Ancient Greeks were accompanied by lyre playing. 'Lyre' can either refer specifically to a common folk-instrument, which is a smaller version of the professional kithara and barbiton, or 'lyre' can refer generally to all three instruments as a family.

Pan flute
The pan flute or pan pipe is an ancient musical instrument based on the principle of the closed tube, consisting usually of five or more pipes of gradually increasing length (and, at times, girth). The pan flute has long been popular as a folk instrument, and is considered the first mouth organ, ancestor of both the pipe organ and the harmonica. The pan flute is named for its association with the Greek god Pan. The pipes of the pan flute are typically made from bamboo or giant cane; other materials used include wood, plastic, metal and ivory. Another term for the pan flute is 'syrinx'. One can still find pan flutes today.

Pandura (πανδοῦρα)
The pandura, or 'pandoura' was an ancient Greek string instrument from the Mediterranean basin. It was a medium or long-necked lute with a small resonating chamber. It commonly had three strings. Its descendants still survive as the Greek tambouras and bouzouki.

Phorminx (φόρμιγξ)
The phorminx (in Ancient Greek ) was one of the oldest of the Ancient Greek stringed musical instruments, intermediate between the lyre and the kithara. It consisted of two to seven strings, richly decorated arms and a crescent-shaped sound box. It mostly probably originated from Mesopotamia. While it seems to have been common in Homer's day, accompanying the rhapsodes, it was supplanted in historical times by the seven-stringed kithara. Nevertheless, the term phorminx continued to be used as an archaism in poetry.

The salpinx was a trumpet-like instrument of the ancient Hellenes.  It consisted of a straight, narrow bronze tube with a mouthpiece of bone and a bell (also constructed of bronze) of variable shape and size; extant descriptions describe conical, bulb-like, and spherical structures. Each type of bell may have had a unique effect on the sound made by the instrument. The common salpinx which is estimated to have been around 0.8 – 1.20 meter long. Needless to say, the trompet is the modern equivalent, although it should be limited to a single note.

The tambourine is a musical instrument in the percussion family consisting of a frame, often of wood or plastic, with pairs of small metal jingles, called 'zils'. Classically the term tambourine denotes an instrument with a drumhead, though some variants may not have a head at all. Tambourines are often used with regular percussion sets. They can be mounted, but position is largely down to preference.
Tambourines come in many shapes with the most common being circular. It was mostly used during the Roman era, but it was not unheard of in ancient Hellas either, and depicted on vases.

A trigonon was a small harp occasionally used by the ancient Greeks and probably derived from Assyria or Egypt. It is thought to be either a variety of the sambuca or identical with it. It was shaped vaguely like a triangle, consisting of a narrow base to which one end of the string was fixed, while the second side, forming a slightly obtuse angle with the base, consisted of a wide and slightly curved sound-board pierced with holes through which the other end of the strings passed, being either knotted or wound round pegs. The third side of the triangle was formed by the strings themselves, or by a column. A small harp of this kind having 20 strings was discovered at Thebes, Greece in 1823. Go with the harp for a mdern equivalent.

Tympanon (τύμπανον)
In ancient Hellas and Rome, the tympanon was a type of frame drum or tambourine. It was circular, shallow, and beaten with the palm of the hand or a stick. Some representations show decorations or zill-like objects around the rim. The instrument was played by worshippers in the rites of Dionysos, Kybele, and Sabazios. In art, the instrument was typically played by a maenad, while wind instruments such as pipes or the aulos are played by satyrs. During the rites of especially dionysos, the performance of frenzied music contributed to achieving the ecstatic state that Dionysian worshippers desired, and the tympanon was perfect for this. The tambourine would be the closest modern equivalent.