If you are itching for something to do you can use the adjective restless. From Cambridge Dictionaries:
moving because you are unable to relax, esp. because you are worried or bored . . . .
Restless can also mean not satisfied with your situation and wanting a change
And the idiom, from MacMillan Dictionaries:
be itching for something/to do something
to feel very impatient because you want to do something immediately
The idiom is most often used when you already know what it is you want to do—the MacMillan example is "itching to get into the kitchen" and your own "itchy feet" is very similar to phrases like itching to get out of the house or itching to travel—but you can stick with the even vaguer "something" if you are just generally bored and restless, modifying it as appropriate.
So for your example, you could say:
I have nothing to do for the weekend, but I want to do something so I am restless.
I am itching to do something (exciting/new/different) this weekend.