Please, I need one for a new recipe.
Grey Poupon
guacamole
Gouda cheese (or Gorgonzola)
grilled chicken
(damn, now I’m hungry)
genoa salami
In my college deli they had a PBJ&G sandwich - the “G” being granola. Probably not what you’d want to throw on a turkey sandwich or anything, but it was the only thing I could come up with starting with G.
Another one
German Butter Cheese
Foods that begin with G
green olive
You know for the garnish. Finish the sandwich, stick in a toothpick with the green olive on it.
gerkin (sp?)
Grasshoppers
Gifilte Fish
German Chocolate
Garbage Pail Kids (what? Like they’re worth anything? Go ahead and eat them)
Gelatin
General Tso’s Chicken
Gary Coleman (he could probably fit)
Gunk
Gin juice
Gorgonzola cheese.
Remember Ally Sheedy’s Cap’n Crunch sandwich in The Breakfast Club? Ewwww.
Then there’s always Goober Grape, that peanut-butter-and-jelly-in-one-jar gunk, but I don’t think that’s quite what lee had in mind. 
oops!
now that i think about it, those are spanish olives huh? Yikes…just ignore me :o
how about green onions?
Great green gobs of greasy, grimy gopher guts.
If it’s anything like the sandwich i made my brother when we were 7 i’d have to say Goober
Upham
Grilled Cheese
Garlic Sausage
Glazed Ham
Greens
Green Onions
Garlic Aioli
Grape Jelly
Gouda
Green Cheese
Grated Cheese
Gravlaks
Game Hen
German Ham
Goose
Grouse
Grouper
But gravlax is much better. And whoever puts it on a sandwich should be drawn and quartered.
Gravy
chique: in fact, gravlax tastes great on sandwich. Ever tried it?
Are you insane? Gramma’d kill me 
Now herring, on the other hand - but that’s an H.
Re the OP: Gherkins, Gruyere cheese, gizzards (gross, but my grandfathers like it), gooseberry jam/jelly
Gnutella 