Hello Mark - well done on entering a Triathlon.
I am guessing you mean fuelling in regards to products ? That's really trial and error and also relates to what speed your BG levels are moving at. I run alot so fuelling for runs means using Hilltop honey (Amazon) for dropping BG levels and if going hypo as it's pretty fast and easy to consume as comes in sachets, so easily carried, I don't get on with gels, they upset my stomach so only in an emergency or at the end for these, to keep levels up during a run it's either glucotabs (a bit dry tho), jelly babies or jelly beans, or dried apricots or dates are good sugar alternatives, then a carby snack at the end to avoid a post run hypo, staying hydrated with water is very important, take advantage of water stations and use electrolytes which are lost through sweat as you can finish feeling quite poorly if your salt levels are low, you can buy sachets of these or use salt sticks from amazon but it's vital to make sure you have this covered.
Keep a watch on levels throughout the following 24 hours too and keep yourself slightly elevated as your muscles do the repair worth then and this can drain glucose supplies.