Hey tolis18nt
I have been wondering the exact same thing about the limit placed on "carried/sideways" cards (hence how I came across your question); here's a reply by one of the moderators to a similar question:
In Munchkin, you can have any number of small (those not marked Big) Items in play, and one Big Item in play. All of those Items you have in play are carried. Of those carried Items, you can normally use (equip) one Headgear Item, one Armor Item, one Footgear Item, and two Hand Items or one 2 Hands Item, and any number of unclassified Items (e.g., Kneepads Of Allure). One-shot Items (those that Item cards that say "usable once only") are Items, therefore they can go into play.
The link to the thread is here:
http://forums.sjgames.com/showthread.php?t=136581
Hope that helps
The Maddest Hatter