Usually nothing. If anything, probably mayo, which I did not vote for as I was thinking about fish and chips, with which I am most likely to dip in tartar sauce.
Other than that, the only thing I know I dip chips in is gravy.
Ketchup is disgusting. I haven't liked it since I was a kid. I also hate American cheese and bologna. I remember once being at a friend's house during lunch time. His mother made us bologna sandwiches with American cheese and ketchup on wheat bread. I actually had to do that thing where you pretend you ate your food but actually spat it into a napkin to throw away.
I didn't even like french fries until I was about 12 years old. Now, living here, I am a chip snob. We will meticulously search for the best fish and chip shop based on their chips and potato cakes and go there alone religiously. Sooner or later, of course, the wogs who always seem to own them sell to stingy asians who immediately ruin everything, and the search continues again. I am only a racist when it comes to food.
Scallops.
But you raise a fair point regarding fish and chip shops. Where about in Aus do you live?