Hi -
Sounds like roundworms. These are white, smooth, cylindrical and evenly tapered at both ends. When they move, they make S-shapes like a snake, without changing length as, say, an earthworm does. Not sure about "very skinny" -- rather thinner than an earthworm in proportion (but not like, for example, a hair-worm which might be 10 cm or 3 in long and only 1 mm or 1/16 in thick).
I think there are several kinds of roundworm in cats, but the ones I've seen are up to about 15 cm or 6 in. Presumably they get them from prey. I've found if they are throwing them up they often have quite a lot. Threadworms (as children get) are similar, but only perhaps 1 cm or 1/2 inch long.
Easy treatment -- a pill, or two pills separated by a few days (can't remember exactly). Not too expensive. Worth doing every few months anyway, as they often get them even when you haven't noticed. Get a pill which will do both round- and tapeworms.
(Poor chipmunks! We don't get those here in UK, only introduced American grey squirrel -- very tasty...).