I just want to point out that if anybody does die without spouse, children, grandchildren, parents, siblings, or nieces and nephews, and doesn't leave a will, everything would go either to more distant relatives or, if there weren't any, to the Treasury. Making a will is not difficult or expensive and worth doing if you'd rather have a say in where your £ will end up.
Also worth mentioning that if you did have none of the above but did have a surviving daughter-in-law or son-in-law or stepchildren you were close to, they would get nothing unless you left them something in a will.
Anyway, to the OP! I really admire the RNLI, who get no government funding at all, and do incredible work saving lives at sea and on major rivers. I'd like to leave them something. The rest of it would probably be divided between my university, a women's refuge and any small charities I'd checked out doing good work in the field of education, working with children and women, health and the environment.