You could always buy cheap panniers like sunlite or Transit for probably close to what it would theoretically cost to rent them. Cheap panniers make great commuter bags once you upgrade to quality bags as well so its not really a lost investment. I also see a lot of used or cheap new panniers for sale on ebay. I think I got my first set of nashbar "touring" panniers for under $20 from nashbar.com.
What other bike specific gear do you want to rent that can not be borrow or rented from a camping store? You can make your own pop-can stove and use pots and pans you already have at home.
How about kitty litter bucket panniers? Maybe set you back about $15!