One of the best tips in travel is to why yourself a second seat when you’re flying coach. Each of the major airlines has a procedure to let you do this, and it can be a great value when fares are cheap. Do it yourself first class, or at least it can be extra room at a value price (and you’re not getting a great meal if you were flying real first class anyway).
The process to do this is different with every airline, but oddly it’s not something U.S. airlines advertise. One airline, though, just made it much easier.