Make sure you eat at least one (1) meal that's of nutritional value, preferably something with protein, because you won't have the energy to do things/be able to focus if you don't eat.
If you're on any medication make sure you take them, try not to take it on an empty stomach unless your medication requires that.
Drink water, if you don't like the taste of it then try gatorade/pedialyte/some equivalent so you are properly hydrated.
Take a five (5) minute break from electronics if possible, let your eyes take a break from staring at the screen. Get up and walk around to stretch your legs/muscles to get the blood pumping.
If it is possible go outside, even if its your porch/backyard, and get some fresh air and sunshine for about thirty (30) minutes.
Most importantly, you are enough. You have always been enough.