Hiya,
I volunteer full time with Sheffield wildlife trust and you can apply for job seekers allowance whilst volunteering (which depending on your age is about £50 per week) as the Trust that you're volunteering at should be able to provide you with a letter stating that you are volunteering in order to gain a job at the end of your placement. However if you're not living at home still then its probably going to be a case of getting a second job to fund your living expenses
Depending on your age and the Trust that you're volunteering with you may be able t claim back expenses. Vinspired offer a volunteering scheme for 16 - 25 year olds with which you can claim back £60/week in transport and food expenses and you also get a training and equipment budget (but it depends if your Trust has placements with the scheme).
Volunteering and Work Experience Placements | vinspired
I hope this helps.