Drink Water! - I know everyone says this, but your body, mind and spirit are going through a LOT and staying hydrated is crucial to staying as functional as you can.
Rest - I know you don't feel like you can...or perhaps you only want to sleep, however take whatever opportunity you can to simply rest, sitting or lying down. If you nod off, good. If not, just giving your body a chance to do nothing is useful.
Ask Others For Help - Even if you don't know what you do need at the moment, do not be afraid or ashamed to reach out to others and ask them for even the simplest of things. One friend of mine simply wanted sheets washed. Ask for whatever you want.
4. Eat! - When David died, a good friend was 'holding space' as the family gathered and all of us in shock and zombie-like, we often forgot the eating part of keeping the body and mind together. "Here Patti-o." he would say, handing me a spoon and a very small bowl, "Just eat this. It's just two tablespoons of yogurt." I was so 'not here' that someone needed to remind me that food was important.
5. Write Down What Seems Important to Remember - If you can, make lists to remind yourself of things that will need to be taken care of in the earliest of days. It is easy to forget those thoughts that flit like bees through your mind that are important tasks to be done.