Nasi lemak (the biggest nasi lemak restaurant in KL is Village Park but it's not in town. I would say it's worth the money.)
Kueh tiao
Nasi kandar
Roti canai
Chicken rice
Laksa (asam laksa/laksa utara)
Nasi kerabu
Nasi kandar
Satay
Rendang
Apam balik
Cendol
Rojak
Otak-otak
Cucur badak
Teh tarik
Ais kacang
The beef noodles restaurant in Petaling Street is popular among locals.
Limapulo is a Perankan restaurant that got recommended by Michelin. I haven't tried but it's worth checking out.
If you're into chili crab you can try out Fatty Crab at Taman Megah. It's halal certified.
Jalan Alor is lowkey a tourist trap lol
Ngl I think the food is the best part of KL lol. KL downtown is farily walkable and you can commute within KL by train but Grab will always be your best friend