Anyone have any ideas on getting a 7 yo to better manage his things? He's constantly losing clothing, toys etc.

Try to limit the items he has on him at all times. Not too many layers, no toys at school, paper sack lunches that can be thrown away, you know that kind of stuff. Good luck

Aside from reducing the amount of stuff he has to keep track of, making a large check-list type thing to hang up in his room (or someplace where he'll see it often) might help. If he's losing things outside the home, have him consult the checklist before he leaves, so he can remember what he needs to bring back when he returns. (Coat? check. Gloves? check. Backpack? check.). If he's losing things around the house, one thing that might help would be limiting certain toys to certain areas. Legos have to be played with near their storage area, the play tool bench and all its stuff has to stay in the family room, board games are played with and kept near the coffee table, etc.

You might want to consider why he's losing stuff. Does it just mean nothing to him? Are his things easily replaceable? Are there any consequences to him losing stuff? If not, make some... If he leaves his favorite sneakers somewhere, he has to wear ones he doesn't like until he finds his favorite ones himself. Lost library book? The fee needs to come from his allowance (or he has to do a chore to pay it off). Lost toy? if you find it before he does, it goes into storage and he can't have it for a while. Sometimes, knowing that once something is lost it is really gone helps a child figure out what to do to keep the things he wants!