The one type of activism that I'm committed to is cycling activism, and bike-related protests tend to be done on bike, so I don't think of them as protests.
I do usually go to Reclaim The Night each year, but in Sydney, it's on the last Friday of October, so it always clashes with Critical Mass. (This in practice means that I end up leading Critical Mass to Reclaim The Night year after year. Yay for joint protests!)
Other than that, in Sydney, the standard time for protests is 1 pm on Saturday outside Town Hall, for various causes such as indigenous rights, same-sex marriage, and some others that I agree with but don't really care too much about. There's usually at least one each month for something. I'll go if I have the energy and have no other commitments. (In practice, that doesn't happen much. I tend to either double-book myself or stay out late the night before and end up sleeping in.)
As a uni student, I get invited to lots of protests. There was a time when I walked past some people with signs and banners on their way to a rally, and I thought, "there's a protest and no one invited me?" even though I was busy with something else at the time and wouldn't have gone to the protest anyway. xD