Any suggestions to keep outdoor plants well watered while on vacation?

Soaker hose on a timer.

I use a kids pool.

Bark chips are helpful in stopping the soil dry out. Give plants a good soaking and the ground should keep cool and moist.

Check with the neighborhood kids, watering isn't hard and I am sure there are a few that are trustworthy enough. Check with the parents to make sure they will not be on vacation at the same time and negotiate a price and conditions such as if they don't do it and something dies what will happen.

Hire a neighborhood trustworthy teen :)

If possible put near a sprinkler and have a timer set for first thing in the morning.Place the plants in the shade and insert empty large soda bottles with the bottom down and insert pin holes sot the water will drain into the plants.

If they are in pots, get a hard plastic blue kiddie pool. Place as many pots in the pool as possible. Fill the pool with water about halfway up the side of the pot.