Following is a list of items you should consider including in your medical kit - consult your pharmacist for brands available in your country.

1   Aspirin or paracetamol - for pain or fever.
2   Antihistamine - for allergies, eg hay fever; to ease the itch from insect bites or stings; and to prevent motion sickness.
3   Antibiotics consider including these if you're traveling well off the beaten track' see your doctor, as they must be prescribed, and carry the prescription with you. 

4 Loperamides or Diphenoxylate 'blockers' for diarrhea' Prochlorperazine or metaclopramide for nausea and  vomiting.
5  Rehydration mixture to prevent dehydration, eg due to severe diarrhea; particularly important when traveling with children. 
6   Insect repellent, sunscreen, lip balm and eye drops. 
7   Calamine lotion, sting relief spray or aloe vera-to ease irritation from sunburn and insect bites or stings. 
8   Antifungal cream or powder - for fungal skin infections and thrush. 
9 Antiseptic, such as povidone-iodine for cuts and grazes. 
10 Bandages, band-aids or plasters and other would dressings.
11 Scissors, tweezers and a thermometer (note that mercury thermometers are prohibited by airlines) 12 Syringes and needles in case you need injections in a country with medical hygine problems. Ask your doctor for a note explaining why you have them.
13 Cold and Flu tablets, throat lozenges and nasal decongestant.
14 Multivitamines - consider for long trips, when dietary vitamin intake may be inadequate.