Simple. And cheap, sure. But also necessary.
Water rides, of course (though not the only reason).
Many theme parks have them (not bags, those you have to provide yourself). To protect your cell phones and any water-sensitive item, just get out the zip-sealed bags.
‘Bagging’ it is always a good policy
Of course, there are many other uses for a bag. Any type of bag.
Your wadded-up, no-longer-chewable-worn-out gum. Given up its elasticity (darn it, just when it got good) when you are not near a convenient trash can.
And even more common: melting ice cream wrappers. These are known for their kid connections, but are also suspiciously common among adults as well.
Just about any old bag of any type will do for the ice cream wrappers, but also for other types of storage in case you did not bring a backpack (slightly cumbersome) or a fanny pack (degrading to the cool-hand image).
But while we are on the subject of the importance of every-day objects when you are enjoying the dream-like magic of theme park make believe, here are some other things to consider:
Did you remember to bring these:
---Plastic, folding ponchos? (Not just for water but rain as well). Featherweight and easy to pack inside any bag.
---A water bottle. Refillable, of course. You never know when you can get dehydrated, particularly n brutally hot climates. Water fountains are not always nearby. And who wants to pay $4 or so for a concession-stand bottle of water, anyway? Remember: not all parks allows your bottle, so check beforehand.
---A money belt? Really old fashioned and dated, sure, and associated with a backpacker’s trip to a crowded Third World city known for its pickpockets. But wait. These usually inexpensive belts are great for safekeeping for any kind of driver’s license, ID cards, etc., even if you don’t use them for money. PS: Pickpockets are probably not much of a concern but the use of a belt might actually save you some money.
Two other suggestions:
You will probably want to keep your phone with you. Most people do. And there are good reasons. But might you consider leaving some stuff behind such as a hair brush or even a comb or even all those credit cards? They should be safe in your hotel room.
Or as an alternative, how about renting a locker? They are always around, and are certainly among the cheapest (read bargains) things you can buy at any theme park.