If you go to the following Website, you can read two theories. Bizkit is obviously "biscuit". I am quoting from this page, these are not my own words:
http://www.amiright.com/names/origins/l.shtml
1. "Limp Bizkit was on Fanatic when their fan asked them how they came up with the name. They explained that they had asked a friend of theirs what a good name would be and he said "I don't know. Right now my brain feels like a limp bizkit."
2. "I heard someplace that Fred used to have this dog named Bizkit. It got hurt or hit by a car or something, so it couldn't walk right. Hence the name Limp Bizkit, b/c it limped around."