It's now implemented, available after the first ranking up. (so if you don't see anything, it's normal : you need to rank up).
You can buy as many as you want of the same item, but only one will spawn with you (so you can do a "reserve").
Right now, it breaks replays, I will work on that later if everything is fine.
You can reclaim them after they go active (not before), that may or not change depending of your feedback.