I love the Listonic app on my phone. It has a list of everything I would buy at the store. One click on the item adds it to the checked section, and once I add the item to the cart, one click removes it. You can even have lists for travel items, or whatever you want. If it's a long list, there is a search feature that locates it immediately.
When I'm doing something, like reading posts on this forum my mind will wander. My wife calls it chasing rabbits. I keep little notepad to jot down all kinds of things. Sometimes its a word that I need defined, or something I should pickup at the grocery, or something I need a reminder to do.
I also use the reminder function on my phone and a countdown widget to keep me mindful of important dates down the road.