sounds interesting. boxes could get heavy for shipping though
I would recommend some minimum guidelines. For example:
Box must contain -
at least 1 bait of the Gen preferred by your partner
at least 1 bag of dollyhair or retrodolls hair (or similar)
at least 1 other *quality* customizing supply that you yourself like and would like to pass on for someone else to try OR an additional bait or bag of hair
if you want to include a custom (and if you do, it should be something all participants have to include), then I think you should add :
at least 1 custom based on your partner's fav gen and colors (leave it broad in theme like that)
participants should list:
fav gen
fav pose in that gen (though they may not get it)
least fav pose in that gen
fav colors (top 3)
least fav colors (limit 3)
and if there is anything you do NOT want to receive (like I would not want any bake clay - I only use apoxie sculpt)