Heat source for winter. You never know when you might need a heat source. This "life hack" is brilliant and simple as long as you keep the necessary items on hand: Bricks, terra cotta pot, tealight candles, matches.
Determine remaining daylight on your hand. Use this simple trick to measure the remaining daylight without a watch. Count the finger widths between the sun and the horizon. Each finger is equivalent to 15 minutes, with each hand totaling an hour.