I have volunteered on a med-onc hospital ward and for hospice. I think they are equally difficult and rewarding in their own ways. There is alot of hope on med-onc, and deep devestation when treatment fails. Hospice is about dying with dignity-the most difficult moments I have had volunteering with hospice is when a family will accept hospice help for financial reasons, yet be completely in denial about the fact that death is imminent, even up to the moment of death.
Learn about the philosophy of hospice and see if you think you can deal with it. Volunteering with hospice changed my life and also helped me to better accept my mothers passing. Being a volunteer and holding the hands of many people as they have passed away has answered many questions about myself and especially my dedication to medicine. I know that I will be a better doctor because of these experiences.
As for what hospice volunteers do, my experience is that you serve primarily as a companion or as a helper. You may run errands, cook meals, or just sit beside the person who is passing (talk, play games, sing songs-whatever makes passing more comfortable for the person.) Usually family members or nurses do the bathing and cleaning, etc. You may also assist the family in many ways; dying is usually more difficult for those who are being left behind.
PM me if you want to talk about this some more. Isid