Maternity pants - How to keep them from falling down?!

Caoilainn • 32, married, polyamorous, geeky artist who loves everything from computers and animals, to sewing and camping.
Ugh! So, I finally gave in at 11wks and switched to maternity pants, as none of my regular jeans were fitting anymore. Actually found some very comfortable and flattering boot cut jeans on sale at Motherhood Maternity for under $30. However, I CAN'T KEEP THEM UP!! [Insert obligatory sexual innuendo here] You obviously can't wear a belt, so how do you keep them from sagging/falling down, especially with stuff like a wallet or cellphone in the back pocket? (I don't usually like tight/skinny jeans, only bootcut/wideleg) Any help is appreciated!