i made a trainer for halo: combat evolved that had infinite shields, inf. ammo, inf. grenades, inf health and armor, and a couple others. i dunno wtf i did with it since i havent played it in so long. ive found trainers that had all kinds of cool stuff in them like super jump, monsters die when they see you, and other neat stuff. just google it or search on CEF.
for the grenades, search under byte. i remember that took me a while to figure out lol.