All dropped packages including health crates, brown crates, and the blue boxes count toward this achievement. An easy way to boost this achievement if you cannot get it by the end of the 20 challenges is to hook up a second controller to your xbox and make a local multiplayer match. Use the controller with your profile on it to collect boxes, but do not kill the worms from the team. On the other controller, make the worms skip turns. By letting the 20 minute clock run out, you should be able to collect quite a few boxes.