I volunteered with my Congressman's campaign my senior year in high school. I was pretty much a "gopher" doing menial office tasks and running errands. I worked a couple campaigns during my college years and moved to more analytical and PR work, compiling poll data, writing press releases, etc. Computers, let alone one with Lotus1-2-3 or a viable word processor installed, were still luxuries at that time, so number crunching was still done by hand and writing was done on typewriters.
Over the years since then I've worked a few campaigns, more for measures than for candidates. Generally I stay more on the "behinds the scenes" side doing support and PR-related stuff rather than the "in your face" canvassing, cold calling and vote wrangling.