What does a mini triathlon mean?
Is it the same as a sprint? 750m Swim + 20k Bike + 5k run?
If it's less than 2 hours duration, most non-diabetic athletes wouldn't bother eating.
An elite athlete would use up to 500kcal of glycogen per hour = 125g of carbohydrate
An average person exercising at moderate intensity would use 150kcal of glycogen per hour = 38g of carbohydrate
Since your muscles contain 300-500g of glycogen, and your liver contains about 70-100g of glycogen, burning 75-250g of glycogen during 2 hours of exercise shouldn't get anywhere near to exhausting your supplies.
If you're really worried, why not put a few jelly babies in your pocket?
Whatever you do, make sure you practice eating whatever you eat during training. If you're not used to eating carbs then suddenly introducing them during a race can easily lead to a "Radcliffe moment".