I don't know what's usually used, but i'd probable use something along the lines of...
what've you been up to? - 今まで何してあるか。 (Ima made nani shita?)
What're you gonna do this weekend? - 週末にしとくの? (Shyuumatus ni shitoku[shite oku]no?)
I'm not 100% sure on either of them, though. Opinions?
EDIT: By the way, you do AT/IN the weekend, you don't do the weekend.
Example: Shyukudai o suru = To do homework