As a kid, I kept everything. Literally everything. Maps and pamphlets from places I visited, various bits of string, rocks I found, any card anyone ever gave me, crappy miniature clay models of food I made once, the list goes on. Like probably everyone, by the time I reached adulthood, I was drowning in objects, more things than were sustainable or practical.
I can’t say if I fit the description of a real hoarder per se, but when faced with the prospect of throwing a thing out or giving it away, every memory that this insignificant bit of paraphernalia and I shared would threaten my brain with disappearing forever if I threw that thing out. That horrified me, as if I were some kind of weird child-creature who apparently subsisted on sentimentality and Oreos. So I kept stuff.
The first time my family moved, I remember my mom remarking to someone that she had once thought I was the neatest and most organized child she had but found out I was actually the opposite, because I had so much stuff crammed into every nook and cranny of my room. My room was actually a chaotic, deeply stacked disaster; I just hid it very neatly, in drawers or boxes or under the bed or wherever stuff could fit out of sight.