Cash in euros is the safest fallback and is accepted everywhere. That said, card payments are increasingly common at beach bars and clubs, especially in tourist-heavy areas like Budva, Becici, and the Sveti Stefan area — many now accept Visa and Mastercard via a handheld terminal.
Smaller family-run concessions on quieter beaches (Lucice, Zanjic, Mirista, Rose) are more likely to be cash-only, so it is worth carrying some notes when you venture off the main strip. ATMs are easy to find in Budva, Herceg Novi, Tivat, and Bar, but can be scarce once you head down a coastal track to a hidden cove.
Tipping the beach attendant is not obligatory but is appreciated — rounding up to the nearest EUR 5, or leaving EUR 1–2, is the local custom at staffed concessions.