What I am about to tell you might change your life. To prevent an avocado from browning, all you have to do is spray it with a little bit of cooking spray. I first heard of this concept on the Epi-Log, but wasn't sure if it was true.
So I tried it myself. I ate half an avocado and sprayed the remaining half with Pam. Then, I covered it with foil like I would normally do with an avocado half. Days later, I pulled the avocado from the fridge and was shocked it see it was not browned at all! Seriously, try this. Trust me. It's amazing!