Many manufacturers of inflatable sleeping pads sell repair kits.
Duct tape could be used in an emergency, but I would only use it as a last resort as it will leave a residue on your sleeping pad when you get back home and want to repair it properly.
Most kits will have something like the following items in them:
- Seam Grip Sealer & Adhesive
- Tenacious Tape Repair Tape or Tenacious Tape Repair Patches
- Small patch brush
Seam Grip Field Repair Kit
If I were to make my own repair kit I would add a few more items to make it a little bit more usable on other things.
- Pencil or Sharpie to mark where the leak is
- Rubbing alcohol to clean the spot
- Cotton swabs to used with rubbing alcohol
- Small pair of scissors to cut tape instead of just tearing it
- small piece of very fine sandpaper to roughen up smooth surfaces if need be so the glue can bound better