I usually use boxer briefs without a seam in front with my packy.. here is a link to a site with some picts of what I'm talking about
:
http://www.urbanbody.com/designer/Clever+Underwear
Not promotting that site, lol.. Just want to give an example.. I guess the best place to find this type of undies would be online or at a "gay boy" store. Most of these undies have a built in pouch so that someone's junk is all cushy and up front.. The cut in back also makes your butt look FANtastic.. lol
I also found these combo athletic supporter/brief at wal-mart a few years back.. that works great.. Jocks with the opening for the cup.. This all helps keep your junk in place, although, the gay boy briefs should be snug and you are still on the loose when you have to use the bathroom..
Just my input
-Tony