I know running is good for fitness, but is there any other things that could help for me to run the full 70-80 mins?

core upper and lower body exercises. you need fitness and strength

try some fartlek training, it's the perfect training method/routine for rugby players, just lots of training at different intensities so sprint then jog etc. other than that I'd just say lots of sit ups and burpees, press ups stuff like that