Repositories are awesome, and we should have more of them.
I recently completed BJ Fogg's Tiny Habits, and it's a pretty lightweight way to install new habits (recommended). However, I realized I could use a better repository of useful habits.
So, please use this thread to suggest habits that you've found useful. Bonus points for evidence/anecdata of usefulness.
Obviously, 1 habit per comment makes upvotes a clearer signal of collective approval.
Paper (especially ink-jet printed paper) doesn't like water, so always make sure your desk isn't wet before putting paper on it, always make sure your water bottle is properly closed before putting it back into your handbag, always make sure the pockets are empty when throwing clothes into the laundry bag, etc.
Always carry a pen, a USB memory stick, a pocket umbrella, a bottle opener, a condom (some of these examples may not apply to you) etc., as you may find yourself needing one without knowing beforehand.
Carry a micro-USB cable - then you can charge your phone from any computer, and use your phone as storage. A penknife will include a bottle opener, a corkscrew and other useful stuff - I'm glad mine has scissors. Carry more than one condom - having only one creates pressure to perform. Pen and paper are useful. I also carry tissues and painkillers.