Theatre Mom here- so everything must be labeled. Clothes and costumes get thrown around, mixed up, moved by others etc. backstage and sometimes they are all wearing the same outfit in different sizes. Pieces get thrown in others bags and boxes, and without names would never be seen again. For any clothes with tags, we use sharpies on the tags. For shoes we write in the shoes with sharpies (we use a silver sharpie if the interior is dark). For clothes without tags we use a piece of masking tape with the name written in sharpie and stick it in the clothes. The problem you are going to have with that is the laundry- I have washed her clothes with the tape in them and had it stay, but it might come off. I think you can find fabric tape or sew in tape that you can write on in sharpie and that is less likely to come out in the wash. I wouldn't mess with the socks. I know the trendy sports socks now can be about $20 a pair. I would try to keep those at home and send cheap socks to camp. I guess if all else fails and the expensive socks are going to camp, I might try to write on them with a lighter color sharpie that won't bleed through to the outside.
Wow- I just looked back at the first post and saw it was from 6 years ago-- those original kids full grown and probably in college now!!!