After leaving the NFL or going to another team, what do players and coaches do with their uniforms/gear and other stuff they may have purchased on their own? Especially for those who have played for multiple teams.
It either becomes personal memorabilia, is donated to charity, or ends up on eBay.
It's my guess that any player who wouldn't want to keep any of their old gear probably knows someone who would like to have it. What happens after that mostly depends on how much they actually cherish it.