In southern Sweden, Swebus express would be your best option. Shops Sweden has no regulated shopping hours, which means that in bigger towns at least some shops will be open all days and often quite late at night. Pharmacies are called Apotek and are the only places you can buy medicines, aspirins etc. There are no drugstores. Post offices are simply called Post.
White mailboxes are for postal giro payments only.
Stamps can also be bought in food stores and kiosks. When sending mail abroad, mark it with the letter A for Airmail and B for surface mail. You have to be at least 18 to buy tobacco. Smoking is not allowed in public buildings, but restaurants normally have both a smoking and a non-smoking area. Otherwise it is OK to smoke outdoors.