If you are traveling alone, find a restaurant where you can eat at the bar. You can talk to the other people and to the bartender. Better than reading at a table by yourself.
Always carry an extra pair of socks and underwear in your carry-on bag. That way, you're somewhat prepared if the airline loses your luggage.
Whether it is for domestic or international travel, carry an extension cord. This helps if you have multiple devices that need charging and means you have to access that inconvenient wall outlet only once instead of over and over.
West Los Angeles
Carry at least three credit cards. Having lost my wallet in Paris, where both of us were carrying the same two cards, we now never travel without three. One is common to both of us, which is our primary, and then we both carry a separate one. That way, if a wallet or purse disappears (for whatever reason), the other spouse still has one card that is usable.
If you carry a reusable plastic water bottle when you fly, you'll need to keep it clean. My favorite vessel is the SoftBottle by Platypus. It's easily filled at drinking fountains post-security check and shrinks in size as you go (collapsing to nearly flat when empty). I keep my bottle clean and mold-free by storing it with the cap off and occasionally rinsing with hot water and a drop of bleach.
Make sure you remove those destination claim check receipts on your luggage upon arrival at your destination. Often they are not, resulting in misdirected luggage. If you check in with those still attached, don't be surprised if your suitcases are incorrectly routed. Best bet is to eliminate any potential mishaps by pulling them off once your luggage is back in your possession.
Playa del Rey
Carry a key ring you can give back. Many car rental companies give you a handful of several keys and an ID tag on a key ring cable that cannot be opened. I carry my own 1-inch key rings, cut the cable and store most of the keys in my luggage. I carry one key. When I return the car I put everything on one key ring. So far, no car rental place has noticed the new key ring.