Don't use tokens to continue runs
Minion Rush isn't like other games such as Candy Crush. You have an
infinite amount of runs and for the most part, getting a super long run
doesn't do anything but boost your top score. You also only need one
fruit item to unlock the next level so if you've already got that,
don't waste your precious Gru tokens. They are always better spent on
costumes, items, and upgrades.
Instead, just start the run over in order to complete it. I can't
think of any scenario where you'd need to cash in tokens to continue a
run, unless you're really having a hard time. However, with the
new Jelly Labs mode of play, most challenges can be completed in
shorter runs as long as you choose costumes and upgrades wisely.