Hot sauce and mustard.

Lots of options, but ol' reliable based on availability is mustard with a bunch of black pepper.

Salt

More fries.

Truffle oil and lightly salt it

Yogurt

/s

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

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.

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.

I find putting things on fries disgusting. I dip.

And my favorites are garlic butter or tzatziki.

Utah fry sauce

Chili, nacho cheese sauce, and diced onions.

Maggi's Hot and Sweet

Heinz 57

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

Sesame

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.

Make sure you're not missing out in joppie sauce

Grilled cheese.