If you go to Montenegro in summer, you will no doubt visit the coast and also the mountains in the centre and north of the country. You therefore need to have a good think about what to place in your bag before you leave!
On the coast (Kotor, Budva, etc.), the temperature is usually between 25 and 30°C in summer: so you need light clothing for the beach and the small coastal towns and of course all that goes with this: suntan lotion, hat, swimming suit, sunglasses, etc.
It is a little cooler in the Dinaric Alps but you can still go hiking in shorts. Sports enthusiasts who plan to walk in Durmitor National Park are therefore advised not to forget their hiking boots, water bottle (the water is drinkable) and everything needed to protect themselves from the sun.
Certain areas (especially Skadar lake) are invaded by mosquitoes and other unidentified flying insects, so do take all necessary precautions! Ornithology lovers will remember to take their binoculars to observe the many birds that live in the national park of the same name.
Lastly, aside from the capital Podgorica, there is no big city in Montenegro, so it is preferable to come with everything you need rather than to count on making your purchases on the spot.