Definitely look for discounts, whether through a grocery store, online, or hotel packages. Do not pay full price.
Parking is pretty insane honestly (cost wise). They do have a nice tram that takes you from the parking lot to the park (though it's not THAT far of a walk otherwise), and it comes regularly. We pretty much have never waited, and we have a stroller.
Food - I would probably do what someone else mentioned and pack a picnic that you can come out and eat. I do know that you have unlimited in/out with your tickets, but I'm not sure if that would cover parking too? I'd have to check. But if so - there are nearby restaurants.
If you do want to eat in the park, just like Disney there are some places that are really pricey and others you can get a decent meal. There is a Subway that costs pretty much what any other subway costs (I believe - it's definitely not far off if it is).
Depending on how much you drink I'd buy the refillable "mug". It's this huge plastic jug almost that you can buy and refill for your trip for .99 a refill. And it really is large.
I know another poster said they check your bags (and they do), but I have always brought in apple slices or almonds, and I always bring a water bottle. They did however question a Gatorade I had once. They let me keep it, but just said it really isn't allowed.
Hershey Chocolate World is SO much fun. My son is 3 1/2, and we have season passes so go often, and he can not get enough of the free ride. Truth be told I've seen it 1000's of times and I still love it. The other attractions in chocolate world do cost money. Oh they have a s'mores campfire thing outside of Chocolate World a lot that is free.
There is one ice cream place (Turkey Hill) that costs less than the other ice cream on property and is a huge serving. I can't remember exactly where it is, but it's there.
Like others have said, the water park is included, and it's fun. They have quite a few fun rides there. Just an FYI - they are (or were in the past) pretty strict about wearing your bathing suit outside of the water area (if not covered by clothes).
Oh and if you have time, they have dolphin shows and a zoo that is also free.
If you like "character" meets/photos there is always a Hershey Bar near the carousel. He/she is usually across from the carousel near some kid rides.
If you have any particular questions let me know - I don't even like rides and I love it there!