Stop eating meat now (if you can) to save resources and trouble. Not only meat is killing (and tastes rubbish to some), it can also kill you. The beef in your burger has already consumed 2 kg of grains and probably 200 litres of water by the time it arrives at your table.
Challenge: kill for meat.
How often do you leave the tap running while brushing your teeth? No excuse even if your tap is broken that wouldn’t turn off.
Challenge: learn plumbing.
Why don’t you eat the leftovers? Save some energy when you cook extra (healthy) food at dinner. Not only it can stretch your dollar a bit, it saves you from tomorrow’s lunch time fast food binge.
Challenge: find leftovers, anything, eat it.
Shower is better than bath. It uses half the water than bath. It’s quicker and cleaner (if you bathe, everything on your feet ends up in your hair).
Challenge: lock your bath room.