You don't need to reserve the item you want, here are 2 quick ways to rent:
1. Build a wishlist of items you want to rent and add to My Box as soon as you're ready to Swap. You'll receive the item at the same time as you return your current Box.

2. Add an item to My Box to soft-book or reserve it for 3 hours while you make a decision on when to Swap. This timer starts when you add the bag to the Box. When the timer runs out, all the items will be cleared from your Box. If you want to add them again, you can find it in your Wishlist Collections under "Box Box Items".