You could do more kind of fitness work you'll do in rugby training
Two that come to mind are:
Set out cones (or markers) 5m, 10m, 15m and 20m from a line, sprint to the 5m, then run backwards to the line, then sprint to the 10m, run backwards to the line, sprint to the 15m etc.etc.
Another is put 3 cones in a line, then lie on the floor by the middle one - get up, sprint to the one of the left - get down on the floor, get up sprint to the far side (10m away), get down, get up, sprint to the middle one again
Also "Fartlek training" - essentially, it's interval training:
Go for a run, but run for, say, 50m, then sprint for 20m, then run again etc.
For example where I live there's lamp posts all down the sea front, and we used to run for two lamp posts then sprint for one
For your sprint training you could start doing it carrying a rugby ball as well - gets you used to running with the ball as it's slightly different to running normally (can't pump your arms as much etc.)