Whenever I have M&S vouchers I never see anything I like for myself!
The last time I had some vouchers I bought a new duvet cover set for my bed and some school uniform stuff...
But this is a good time of year to get some new clothes for yourself - all the spring/summer stuff is coming in.
If you are on a diet how about getting some clothes in the size you are aiming for to give you an incentive?
Or get some new summer shoes/sandals