When we go on trips I save receipts, a drink coaster from wherever we ate, the little things that remind me of the memories we made.
I do try to pick up a key chain from every place we go. I hang those on the Christmas tree. Those are another trip down memory lane. Does that count as a collection?
When I was younger I collected barbie trading cards. I never traded them though. I'd bet that my parents still have them in the basement somewhere. I had a big poster that listed all of them and I'd check off the ones I had. I probably had at least 75% of them. I would constantly get them out and sort them out. I sorted by year, by outfit, by barbie in the picture. The back of the cards had facts about the outfit in the picture and the year the barbie was released. I probably had those memorized at one point during my childhood.