If you have reached this point, you should have already accessed the supermarket by joining the handle and the saw so as to do so. Unfortunately, there are no drinks at the supermarket, so you have to keep searching. Open the map and head towards the "Hofbräuhaus" brewery. Once there, on the counter, you will be able to get some drinks.
In this case, drinks will NOT become part of your inventory, but you will get notified of your next mission on top of your screen: recharging the radio. Good luck!