Use a scratch pad or notebook next to you (a real paper one). Use this as a braindump, just what ever comes just jot down, todo's, ideas etc. This way you can concentrate on the task at hand and throw anything else in here.

Think of it like a swap space for the brain.

And at the end of the day/task, make a note on what to accomplish the next time. This really takes the stress of remembering a lot of things.