I try to visit a shelter everytime I go out of town and in my experience, the majority of donations are for the benefits of the dogs, leaving the kitties out
WalMart and other big stores often accept food donations, so the overlooked items often include towels/cat cushions, cat litter & boxes (*they don't always have to be actual cat boxes - storage boxes, which are cheaper, are often accepted & the cats prefer the large sides). I also include lots & lots of disposable gloves, bleach and heavy duty trashbags - which are greatly appreciated.
I also contact the local carpet stores for donations of unwanted carpet samples - you'd be AMAZED at how delighted the carpet stores are not to throw them away AND how glad they are to help out!!
The shelters like them because each cat can have it's own carpet to enjoy and to take with them!
Bless you in your mission of sharing the goodness and joy of the season