I had my players once fall into a giant underground lake that was home to a Dragon Turtle. The intent was that they would have to fend off the best while trying to get ashore because they were too low level to actually defeat it.

One of my players just so happened to have a Feather Token for a Swan Boat, which they used to trivialize the encounter and get to shore before the monster could reach them.

The only reason she had the Token was because I had given them all a few thousand gold to buy magic items with at character creation, and she had decided to buy a bunch of random consumables instead of the normal +1 weapons and armour. And the best part was that she was a very new player and probably didn't buy the Token with any actual consideration.