There really is no quick and easy permanent fix for holes in a floor pan. Ideally, you're going to want to determine how if it all the holes are affecting the structure of the car. In my experience, if you can see this kind of damage there is likely a good deal more rust you can't see.
To get this correctly fixed, the rust will have to be removed, fresh metal welded in, and properly sealed. Some people take their chances with fiberglass patches, but there do little to nothing to restore proper structural rigidity to a rusted floor.
I have a '97 Cabrio that developed rust around the two rubber plugs in the rear floor. Eventually the plugs fell out as well. I have used fiberglass in the past on another car for patch panels and it was a failure. The fiberglass let go after a few months and the patch came loose. I have used pop rivets on another car and that worked but the patch was not water tight. I would have MIG welded the Cabrio patch in but I did not have a MIG welder and could not drive the car b/c in order to expose them for welding the whole interior had to come out.
With an adventurous spirit I bought two part "body epoxy" (adhesive) and the special caulking gun it requires from a pro-paint and body shop supply store. I cut out the rust and cleaned up the edges. I made a patch that matched the shape of the floor there with a body hammer and a piece of wood to shape it over. The patch overlapped the metal 1/4" all the way around the hole in the floor. I cleaned off the paint around the hole inside the car. Notice I did not have any rust to clean off because I had cut the steel back maybe 3/4" around the rust to get clean steel. I traced the shape of the patch panel on the floor and then applied the epoxy and spread it around the patch panel's pencil lines on the floor. I put heavy steel weights on the patches and waited 24 hours. While it dried I cleaned the squeezed out goo with some lacquer thinner and a rag. I also added more epoxy to fill any gaps between the patch and the floor from below. Once dried I sanded the epoxy a little and the patch and brushed on Rustoleum paint. Not sprayed.
The patch has remained solid and rust free now for three years. I would do this for door bottom patches and floor patches or lower fender patches no sweat. I would not do this for anything structural such as suspension mounts!!!
Trust me when I say that the discount auto parts stores are not going to have any products similar in quality. HONEST.