Counting out exercise books and rationing pencils are not going to make a big impact to the budget. To do that you need to trim your biggest costs and make sure you are getting every pound of funding, including pupil premium, you are entitled to.
Staffing is always going to be the biggest cost. If things are desperate then redundancies may be necessary but should only be an absolute last resort. In recent years TA provision has been reviewed and the headcount reduced in my school. We have also have between 9 and 12 classes dependent on numbers and that reduces teachers.
As pp say, renegotiating contacts and suppliers to save money can help. We have had big savings by changing energy supplier.
How easy is it for your parents/carers to claim PP at your school? How often do the reminders go out? If it's too hard to apply some people just won't bother.
Our after school club makes a reasonable amount of money for us but charges a low cost to parents. We also get a small income from hiring out the hall to exercise classes, Slimming World and school holiday clubs. It's not loads of money - about £12,000pa for the whole lot. Or a third of a teacher 
That's not to say having a general green agenda where resources are used carefully isn't sensible. Power use, in particular, can make a significant difference to energy bills. Are things being switched off at night? Fans and air con are some of the worst for consuming electricity and lots of small screens left on add up to a reasonable amount of use over a year... but it's a drop in the ocean compared to the other stuff.