Blood sugar should be monitored frequently.  If you are travelling with someone who is diabetic, learn how to use their glucose tester.

Plan meals with as much routine as possible.  Have food and water available and encourage frequent snacking.

Have a backup source of insulin and consider carrying injectable glucagon.

People with diabetes are more prone to cold injuries (hypothermia and frostbite) and infections.

Cuts and blisters should not be ignored.  They should be cleaned thoroughly, kept clean and monitored closely to avoid infection.

Illness can be much more serious for diabetics.  Significant vomiting or diarrhea and inability to hold down food or fluids is cause to seek medical attention.