When I first started doing this (back in the 1970s when I first got my driver's license) I was scared to death and did everything I could to conceal them--sweat pants and a long coat--and still, I was positive that everyone within a mile of me absolutely knew I was wearing diapers. But the older I get, the less I care.
These days if I do it in the summer I just pull on loose fitting shorts over my plastic pants. In the winter I wear sweat pants over them. If I'm really feeling daring, I wear tight sweat pants (which makes my thick diapers totally obvious) or, sometimes, a pair of white air-mesh shorts with the liner removed that you can almost see right through. It seems like the longer I'm out this way, the more comfortable with it I get and the more daring I become--for example, I'll pull the top of my plastic pants out of the back of my shorts and stuff my t-shirt in there then act like I have no idea that they're showing.
I just love the way middle-aged women will notice, their eyes get big and they get this big grinning "I can't believe this!" smirk on their faces.
I also have a t-shirt that says "I (Heart) Wet Stinky Diapers". I've never had the courage to go out diapered with that on, but maybe one of these days.
I should note that I only do this once or twice a year, in the morning, on school days, between around 9-Noon because I really try NOT to be seen by kids, and I don't much like being noticed by other men, either.