You could do the gift cards as many do, or if you have a trustworthy arrangement you could supply funds in advance in either direction.
There’s also putting spare change in a 5 gallon container, in which case your SO will praise you for being thrifty.
Or perhaps put on your grungiest clothes and get a sharpie and a cardboard sign.
Collect cans, sell scrap metal, hold a garage sale, sell blood plasma which would involve you lying on your back for about an hour.