Keep in mind that some ammunition just doesn't work very well on machines. For this reason, you may want to keep a rack of rockets in reserve, for use vagainst mechanical foes.
Having to re-trace your steps and find the carrot you missed, when you're at the end of a level, can be quite an ordeal. Be very, VERY careful when searching mazes and tunnels.
Don't miss the little birthday presents! Changing your armor is sometimes useful, and always amusing.