Cooked barbeque sauce.

None of that raw shit.

spicy mayo, but sour cream isn't bad either

I picked up a love of curry sauce or garlic sauce on my fries during my time living in London.

Those folks do fast food right - cheap, easy to find, and greasy.

Hot sauce and mustard.

Sauce Remoulade. Or Sauce Mornaie (SP?)

Rogan josh curry sauce (although most other curry sauces are also good). Chips and curry sauce is a really popular fast food in the UK, but the curry sauce in question is much closer to a brown sauce than it is to anything that's usually associated with the word "curry". So I make my own curry sauce and put it on instead. This does, of course, completely ruin the "fast" part of "fast food", but it is very tasty

Maggi's Hot and Sweet

Au jus. When it comes with something else I dip the fries also.

Yogurt

/s

Truffle oil and lightly salt it

Shoarma or döner kebab, cheese, garlic sauce, a bit of sriracha or sambal, and some greens.

Or if I'm feeling simple, mayo and a bit of mustard.

Heinz 57

Make sure you're not missing out in joppie sauce

Sesame

Grilled cheese.

Utah fry sauce

I find putting things on fries disgusting. I dip.

And my favorites are garlic butter or tzatziki.

On fries I really only do ketchup. I use Sriracha on almost everything else that's primarily potato, but not fries. I used to use A1 steak sauce every so often a while back. I hadn't thought of that in years; might need to go pick up a bottle.

Best thing I've ever had with fries was the pepper sauce they have at some "Frituurs" in Belgium. Can't really get that here in Germany unfortunately.

Salt. Ketchup is for kids or for eating cold, overcooked, and/or shitty fries.

Chili, nacho cheese sauce, and diced onions.