"When making our kathiskos, should we limit the food stuffs to less perishable items? I eat a lot of cheese and would rather not have a jar of honey, oil, water, and cheese sitting in my pantry for a month, I'm sure you understand. What do you think of a refrigerator kathiskos?"
The kathiskos is an offer jar of foodstuffs used to protect the household’s food storage. Typically, it has olive oil and water; the rest is up to the household. The kathiskos is dedicated to Zeus Ktesios, guardian of the household. The jar is typically emptied into the compost bin or garden and refilled with fresh foodstuffs every month, on the Noumenia.
The ancient kathiskoi were often unsealed, and I suspect that sometimes they would be tossed earlier than the new Noumenia or ingredients were carefully selected. Personally, I don't know anyone who has an unsealed kathiskos these days, because most Hellenists I know enjoy the tradition of keeping it for a month.
in all my years making a kathiskos, I have never shied away from using anything, and the worst the content of the kathiskos did was that the water turned a little murky. If you seal it up air tight, you wont have much of a problem--until you open it, of course. But I like to think of it like this: all the rotting and fermentation that took place in your kathiskos did not happen to your other foodstuffs. The worse the smell and the worse the status of your content, the better ;-)
"Hello! On your blog is says that the Panathenaia is from the 23rd of hekatombaion to the 30th. Does that mean it ends before the 30th begins or does the festival include the 30th day?"
It includes the 30th, unless the month only has 29 days, then the festival includes the 29th day, but doesn't stretch on into Metageitnion. The Greater Panathenaia includes the 30th, the two Lesser Panathenaia in-between include only the 29th.
"Would it be 'allowed' (seen as non-disrespecrful I guess) to make one alter for more than one god/goddess? Or are alters and shelves reserved for one theos only? Thanks :)"
Most shrines in ancient Hellas were, and even during festivals for a particular Theoi others were worshipped, so I don’t see why not!
"Is there a greek god of finding missing things?"
Not as far as I know, but in general, Gods and Goddesses whom you have built kharis with will help you when you are truly in need. From a purely personal perspective, Hermes would most likely be able to find your items, seeing as he’s been known to hide (and steal) items Himself ;-)