Do you want to give people a way to make a donation on your registration page without setting up peer-to-peer fundraising?
You can do that with a Donation Box.
A donation box is an open box which will let people make a donation of any amount on your registration page; the donation will be added to their cart total when they check out.
You can set up a donation box by clicking Merchandise on the Event Setup menu; then, click on the Add Donation Box.
Enter the details of your donation box, and an image if you'd like; then, hit 'Save,' and the donation box will be added to your page.
Anyone can make a donation on your page whether they're registering for the event or not.