Id say I generate about 3/4 tablespoon of belly button lint everyday. Its hard to measure by volume bc its so fluffy and voluminous. I notice it when I come home from work and change, my belly button is just full. Sometimes I like to extract the lint and leave it in funny places so my wife notices it. She is amazed at how much I can produce; she has never seen belly button lint production like mine. Its kind of a proud manly moment for me.

I do notice I make the most lint with cotton shirts and produce even more when Im moving all day and presumably my belly hair rubs more against my shirt. Synthetic fabrics make less lint for me. When I use bright colored towels, the lint has a tinge of color from the towel. Otherwise its mostly the color of the shirt I was wearing.
My dad is also a heavy lint producer as we have the same stomach body hair pattern that swirls around the belly button and I hypothesize channels the hair into there. I get lint in my butt crack like this too; again a hairy place with cheek hair all pointing towards the same direction of the crack.