Instructions
Either buy or build a cricket bin. A plastic storage bin can work fine for this, but make sure to puncture several small holes in the top to let fresh air in. A wooden box or an aquarium with a screen over the top can work just as well.
Crickets like to bundle and hide, so take egg cartons, toilet paper rolls, and paper towel rolls and lay them all around in different positions in the bottom of your bin. This will also make it easier to catch the crickets when needed.
Keep the bin warm at all times. If you can bring it inside, that's perfect. Otherwise, you can try to use a heat lamp to keep the bin at around room temperature. Make sure to connect the lamp to a timer so it will only go on only for short bursts -- high heat levels will kill the insects as surely as freezing temperatures will.
Slice up whole potatoes into fours and place them all around the bin. This will supply food for your crickets.
Place a small container in a bottom corner to keep water for them. Don't just fill a bowl with water, though -- the insects will drown in it. Instead, try using damp paper towels or use gel beads that hold water. You can typically find them in the gardening section of your local hardware store.
Place your crickets and you're ready to go. Check their food and water every other day.
How to Keep Crickets for Fishing
You don't need a fancy setups to keep crickets alive for your next fishing trip but, depending on how long it will be before you need them, you will have to make some provisions for them. Food, water and air, of course, are their primary needs, but the insects need these things to be presented to them in particular ways if you want to keep them alive.