https://www.lahudky.cz/nase-prodejny/ (web is in Czech)
Want to try typical Czech delicatessen? In the branches of this chain "Libeřské lahůdky" you can taste typical Czech "chlebíčky" (open sandwiches) as well as "koláče" (round flat pastries with fruit topping) and some typical Czech sweets (rakvička, makronka, větrník, laskonka, ašant), Czech "buchty" (sweet filled yeast-dough buns).
One is next to the Wenceslas Square, at tram stop Vodičkova.
When you visit Czech pubs, you should try these:
Slivovice (plum brandy from Moravia)
Pilsner Urquell (lager)
Becherovka (herbal liquor from Carlsbad)
Kofola (non alcoholic, communist alterantive to Coca Cola, citrus flavoured)
U Fleků https://en.ufleku.cz/ (Well known thanks to the novel "Good Soldier Schweik". One of the oldest continuously operating restaurants in Prague, over 500 years old. Eight halls plus a garden.)
U Pinkasů http://www.upinkasu.com/ (Pub garden in an unfinished nave of a medieval church. First Pilsner pub in Prague)
U krále Brabantského https://www.krcmabrabant.cz/en/ (a stylish medieval tavern, waiters in costumes, dark with candles)
U zlaté studně https://www.terasauzlatestudne.cz/ (eating on a roof terrace with a great view of the historical city center)
Velkopřevorský mlýn https://velkoprevorskymlyn.eu/ (you can eat in a garden with a view of a giant wooden wheel of a mill)
This is how working class was eating during the communist regime. If you want a budget self-service cateteria where you carry food on your tray, there several places to go.
Jídelna Světozor (Vodičkova 39, Praha 1) - at tram stop Václavské náměstí (in the passage Světozor)
Lidová jídelna Těšnov (Těšnov 1163/5, Praha 1) - at tram stop Těšnov near Bus Terminal (very budgety, original 1980s look)
Havelská koruna (Havelská 501/23, 110 00 Praha 1) - between Wenceslas Square and Old Town Square