I'm sure you've seen this on Pinterest, but it's kinda changed my life where watermelon is concerned.
Cut it into cubes. Not triangles. Why does this matter? I don't know but suddenly everyone in the house is eating watermelon. It's less messy, more fun, and there's somehow less waste.
I've also found the little watermelons work best for my family. Big ones usually result in 40% waste. We get sick of it and then it gets weird hanging around on the counter or in the fridge.
So: baby watermelons, cut into cubes.