IMPORTANT: When selling items, do not exceed 20. You will begin losing items if you sell more than 20. Text Tutorial Below.

==================
Notes:
1.) You need to be in an area with a vending machine to do this.
2.) Do not sell more than 20 items. Exceeding 20 items will result in the loss of your item.
3.) If you do lose an item when selling, you can revert to a previous state by going to the Dashboard (quitting without saving) or signing out of your profile. You can then restart the game, and you will be reverted to a previous state.

This is the result of a bug with the Buyback function of vending machines that causes items to stack on top of your current inventory (rather than being added to the total) in the same way that Quest items/weapons work.
This trick can be done to allow you to carry a maximum of 47 items at once.
To do this, pick up everything you can (or start with a full inventory). Find a vending machine, and sell some of the items (You will be buying these back later).
IMPORTANT: DO NOT SELL MORE THAN 20 ITEMS. If you exceed 20 items, you will start losing items (the vending machine Buyback only lists the most recent 20 items).
(For each item you sell, you will be able to carry 1 extra item.)
Once youve sold some items to create room in your inventory, return and pick up the remaining items you wish to carry. Once everything is picked up, go back to the vending machine, and Purchase all of your items from the Buyback option. The items you re-purchase will stack on top of your current inventory, allowing you to carry up to an additional 20 items.