gosh I’m missing Poland so much as I write this! I will definitely want to visit Poland again!

In Poland you should try the honey beer (Ciechan Miodowe in polish)! It is damn nice! I Along the backpacker alley in the old town of Krakow there are several bars offering affordable prices for flavoured vodka or housepour shots  (1€ each cheap cheap!) There are many nice flavours, such as walnut, apple, honey which are some of my favourites. 
Notable dishes to try would be pierogi (polish dumplings), placki (potato pancakes), sour cabbage soup, meat and rice wrapped in cabbage (polish food with lithuanian influence)
There is also an option to join the free walking tour in these two cities, conducted by locals and at the end of the tour, just tip them whatever amount that you feel comfortable with. 

Warsaw
eat: Bar Bambino. Krucza 21, Warszawa, Poland.
go to “Bar Mleczny” which is the old communist type of restaurants, don’t expect service, fuss-free food
My host recommended me: Museum of Warsaw Uprising – it’s very modern and quite interactive
Copernicus Science Centre (http://www.kopernik.org.pl/en/). It’s a kind of interactive museum with experiments according to physics, body, mind etc. (it’s not for children).
I didn’t have time to go to the museums, instead I walked around the old town, eat pierogi, saw the uprising monument, the president’s palace, ghetto neighbourhood.
yup nothing much in Warsaw in my opinion, I preferred Krakow.

Krakow
Walk to Wawel castle, which offers nice views of the city as it is perched at the top of a hill overlooking the city. 
I also went into the cathedral, admired the nice ornaments. 
If you have extra time, you can go to the salt mines, otherwise Auschwitz and Krakow in 3 days is just nice.

restaurant: Gospoda koko on golebia street
decent food at cheap prices ~6-8€ for a filling dish
don’t eat at the restaurants in the old town facing the square – they are expensive tourist traps. 

Krakow-Auschwitz
There is no need to sign up for a tour unless you are lazy to plan or take your own transport. It is 1.5h bus ride from Krakow to Auschwitz, with several departures everyday. 
Find the minibus (12zl) from the basement of Krakow’s Dworzec Glowny, bus station towards Oświęcim (polish spelling)
Then pay 30zl for the entrance fee to Auschwitz with an English speaking guide, it is not possible to walk around on your own unless you want to wait until after 3pm, but I think the guide would be useful in explaning stuff.
Then take the free shuttle bus to Berkenau which is another concentration camp site around the area, but much bigger.
Actually spending  4-5h in Auschwitz is enough to cover everything, most of the rooms are quite empty except for some info panels to help you imagine what life was like during the war. 
The bus timings back to Krakow are not so frequent, about there is about 1-2h wait for the next one. I took the 4pm bus back to Krakow.

voilà hope this helps!