I wear boxer briefs 99% of the time and occasionally boxers. When I wear boxer briefs the elastic usually sits right on my hip bone or slightly above (but then, I really hate the feel of low rising/low cut underwear, so its just a personal thing for me. But there are some boxer briefs that are made to sit lower). Most boxer briefs will hold a packer without fear of it sliding out.
I prefer Fruit of the Loom.