I took some time off between jobs and didn't work between April and July of this year. I was a Beto supporter early on and had half-heartedly looked for ways to support the DNC in general, but all I ever saw on their site was info about giving donations. However, for the first time in forever I actually had time to give, so I dug around on Beto's site and found a volunteer form with a bunch of ways I could use my time to help his campaign. I picked a few things I thought I could help with and filled out the form. The next day I hopped on a training call with a Beto staffer and the day after that I started sending texts for them. I think back to those early days and how SO many people I talked to had no idea who Beto was, and now he's neck and neck with Cruz. I haven't been able to do much since I went back to work, but I do think every little bit counts.
My general advice is that if you don't just want to donate money, go poke around on a specific candidate's site and see if they have volunteer opportunities that make the most of the time you have to give. They will always push donations first, but usually in-kind opportunities are there, especially if it's a grassroots campaign.