Like B and C said, and I learned this from a nomad named Sunny Skies: remove as much outer packaging from purchases as is practical, before leaving the store premises. Deposit this in the trash can outside the store (they always have them at Wal-Mart, for instance). I even have plastic egg containers, which help keep my eggs from breaking on rough roads, so if I've just purchased eggs at a health food store I simply give them back the carton. One does become very trash-conscious when boondocking, which I feel is a huge plus.
The Dire Wolfess