It's not always hot and sunny in the summer time. So, it would be wise to take a sweater or a jacket with you, as it can be cold in the evenings or it might rain during all day.
Photo Equipment: Don't forget to take your photo camera. The sunsets are just wonderful here, as well as some other touristic spots.
Even when you visit in peak season in summer, keep in mind that there can be strong winds and rain. So bring a wind stopper or rain jacket and umbrella. You may be amazed to see people swimming in the sea whereas others are packed up quite wind proof.
Toiletries and Medical Supplies: Sunscreen, beware of the wind!
Photo Equipment: If you have a digital camera you may want to make sure you have enough batteries or your battery charger with you. I had to sun around several shops to find Lithium batteries and the vendor said that I was buying the wrong one (which wasn't true), it was the only one in stock. So be prepared.
Miscellaneous: Note that some public toilets only give very little toilet paper. You may find it a good idea to carry a bit on you.
Toiletries and Medical Supplies:
If you are coming to Palanga for a private accomodation, don't forget the towels.
You will not find it on toilet, in 90% of cases.