Asklemmy

I live in Alexanderplatz and I work in food. The area is mostly tourist traps (bad ones at that, we are in Germany, not in Italy). If you want something very casual, Bahn Mi Stable is the closest decent thing from Alexanderplatz. If you want a proper sit-down restaurant try Trio (German), Soopoolim (Korean), or Pizzeria Standard on Torstr.

Ignore completely the reviews on Google Maps or tripadvisor, they are totally unreliable.

If you want touristic stuff, the city center is quite boring but you have a lot: museum island, branderburgertor, Gendarmenmarkt, Checkpoint charlie and all the surrounding areas. If you want something more interesting, the Soviet Memorial in Treptowerpark, Victoria Park, the various memorials in Hellensdorf. Also avoid at all costs the DDR museum, lamest waste of money you can think of. Other museums in the center are ok.

Most places that accept card also accept contactless, but there are plenty of smaller shops still not accepting anything but cash. Common offenders are street food places, spätis (little shops selling mostly drinks/alcohol and tobacco/nicotine), bakeries, ice cream shops and the likes. Bars sometimes take card, but it's always a gamble if you don't know. Ask before ordering, if you don't see a sign. I think all supermarkets offer card payment.

The only food recommendation I want to give is my favorite Döner place. I've shown a bunch of my friends and most say it's the best Döner they ever had and that I've ruined other Döners for them by showing them that one lol. Downsides are it's a bit expensive (8€ Döner), it's a bit of a ride from Alexanderplatz (~45min), and they only take cash. I think it's all well worth it. edit: Somehow forgot to mention: the place is called Golt'z Kebap.

Absolute must see for any kind of nerd is the Technikmuseum, and the Video Game museum is also pretty neat. They have a bunch of old arcades that you can play on, and one of them has a vector based CRT screen, something I've never seen, being somewhat young. There's also a mechanical keyboard shop that I've been meaning to visit, maybe that could be a destination if you're into that (Geekboards). My favorite Parks are Wuhlheide, Treptower Park and Park am Gleisdreieck, in that order.

Hope you have a nice stay! Let me know if you want to grab a beer or smoke a joint with a fellow lemming

Not a restaurant, but head over to Cafe Buchhandlung and Zosch - two bars in the area which still have the old Berlin vibes