The good thing about an Altoids tin — besides that it helps contain curiously strong mints — is that it's so portable. Fill it with foil (if you have it) and fuel such as wood or cardboard. Light the fuel, close the lid, and use the tin as a mini-frying pan. Learn more here.
Cut the top off of a plastic bottle, stick some food inside, then invert the top as pictured above. Fish will easily be able to swim inside to snag the food, only to discover that they don't know how to leave.
If you're desperate and stuck somewhere without a main water source, like a river or lake, hope is not lost. Use a shirt or cloth to soak up ordinary dew, then wring the water into your bottle or makeshift bowl. It'll take time but it'll get the job done.
If you're going to be stranded in the wild for a while and you are not much of a hunter, let the prey come to you. When the game bumps into the balancing stick, the cage will fall on top of them and you'll be able to live another day.
Remember that scene in Castaway where Tom Hanks had to knock out his own tooth? He might have been able to spare himself some pain if he just had acorns. Crush some acorns and boil them in water, then use the brew to rinse out your mouth. The tannic acid will soothe your toothache and also works as an anti-inflammatory.
You'll need two containers and a piece of cloth. Fill one container with the contaminated water and leave one empty. Connect the two with a piece of cloth and after a while, the water will migrate into the empty jar, mud-free. Make sure to boil the water before drinking. Learn more here!
Hold up your hand so that it looks like it's just under the sun. Your fingers roughly represent 15 minutes, so your hand roughly represents an hour. This will help you decide when to focus on searching for help, and when to focus on finding shelter.