Volunteering is not only a great way to do something interesting and useful, but also the simplest mean to remove accommodation and/or food costs, and find friends among locals and travellers.
Living on the road you don't want at all go for tours and museums all the time. In my case, i like to be busy working but not working, doing something i enjoy while learning something new, and creating something that will stay when i go.
My volunteering experience started only after 6 months since the beginning of the travel, in a bar of a party hostel, where i got free accommodation, a meal a day and, as you might guess, a bunch of free drinks in exchange for 4 shifts/week. I also had a plenty of free time, because most shifts happened in the evening/night, so for the rest of the day, i could explore everything i wanted. Since then i tried and learned many things in exchange for accommodation and/or food - from making a website for an NGO to building a clay house. Workaway.info gives you plenty of options and areas to choose from in various locations (HelpX.net and Worldpackers.com as well) - check it right now!
But, in my case, most of the volunteering i found by myself, just by asking or offering help in places, where i liked the cause, the vibe and the owners. Like this you can be sure to stay in a place and with people you feel totally comfortable, enjoying each and single minute of your volunteer time, which usually is limited to 4-5 hours/day, 5 days/week. It also helped me to avoid places, where volunteers are taken just to have an almost free work-force.