Set up your ladder in a safe, securely locked position that allows easy access to the loose gutter nails.
Remove one of the gutter nails, prying with the claw of the hammer if necessary, and drop it into an empty pouch on your tool belt.
Coat a toothpick in wood glue and jam it into the hole left behind by the nail. Repeat with several toothpicks until you have completely filled in the hole.
Cut the toothpicks so they are flush with the surface of the house. Trim the ends with a utility knife to achieve the right length.
Allow the wood glue to dry. You can move on to the next nail or wait to do one at a time, but remember to leave enough nails in to support your gutters.
Place a fresh nail over the newly sealed hole and tap it in with a hammer. Alternately, replace nails with wood screws and drill them in with a power drill for extra security.