Put a +1/+1 counter on each of up to two target creatures.
Flashback {1}{W} (You may cast this card from your graveyard for its flashback cost. Then exile it.)
If Travel Preparations targets two creatures, and one of them is an illegal target by the time Travel Preparations resolves, you’ll still put a +1/+1 counter on the other creature.
You can’t target the same creature twice to put two +1/+1 counters on it.