Ella and Jack are both microchipped, but I like to keep tags on them just in case. They're home alone during the day, so I got them breakaway cat collars. I have 5 now, for variety
I get them at Petco--they're called "The Saftey Collar" (it was important to my bf that they didn't say 'cat' anywhere). I think they're about $7 or $8.