Very simple, but in case someone doesn't know:
Use "thanks" as a reminder when asking someone to do something. Two examples:
Me to a friend at 10:00 pm last night: "Can you pls send me such-and-such a document?"
Him, 10:05 pm: "Sure, I'll send it to you when I get to the office in the morning"
Me: *leaves message unread*
Me, 9:18 this morning: "Thanks so much!"
Him, 9:22 am : "Np, just sent you the file via email"
_
DW, one afternoon: "Can you pick up bread on your way home from work?"
Me: "Sure"
Me: *promptly forgets about it*
DW, when I'm typically driving home from work: "Thanks!"
Me: *turns around to stop at bakery*