From SecularPortal

There are lots of ways to raise money to fund society activities.

Sponsorship

Sponsorship has the potential to raise large amounts of money but it is often hard to find companies or organisations that are willing to sponsor free thinking organisations because they are often classified as religious.

There are a few organisations which specifically do fund these types of activies such as the Richard Dawkins Foundation, Secular Student Alliance and Atheist Alliance International.

Donations

Another good strategy is to seek donations from public figures. The trick is really to send off letters to absolutely everyone you can think of (especially alumni of your university who have gone on to better things). Be nice, polite and stress that you are (presumably) filling a niche on campus. Try everyone you can think of, especially MPs and Lords; one donation could fund you for a long time! Always be courteous and not too grasping, and try and offer them something in return. They could speak at your society, become a patron etc etc.

Cake sales

Cake sales are a student society fund raising classic. They are fairly simple to do in that you simply bake a load of cakes (or if you are feeling overly lazy buy them in), set up a stall around your student union and wait for people to turn up. And they will.

That having been said, they don't tend to raise huge quantities of money - usually less than £100, often significantly less. For example the the first cake sale Leeds ran raised £50 after out initial costs had been taken out and we have a fairly popular union.

Also you need to make sure you have a lot of cakes. Say for example if your average selling price is £0.40 and you're hoping for a net revenue of £100, the maths says you need to have 250 cakes.