If you are going to Sri Lanka, a small first aid kit will not be burdensome for you, but it can be important enough for you to feel calm in a tropical country and, if necessary, could provide yourself with first aid.
In the first place among the necessary medicines, I would put funds for sunburn. Unfortunately, burns are not uncommon among tourists and require special treatment. Also on the trip you will not be disturbed by mosquito repellent and psilo balm, which will help you relieve inflammation and itching if someone bites you.
You can also bring bactroban, streptocide, peroxide, plaster, manganese, analgin (or other pain reliever) with you, and for women, I would advise you to take personal hygiene products with you (pads and tampaxes, the latter simply do not exist here).
At the same time, I want to emphasize that Sri Lanka is a fairly clean country, there are no dangerous diseases here, and tales of the annual epidemic so far, thank God, remain fairy tales, even if they come from the lips of high-ranking Russian officials. There are many pharmacies with a large list of medicines, many hospitals with good Japanese equipment, and normal doctors who were educated most often in Russia or England.
So, be healthy !!! And come and visit us!