Family travel on $150 a day

Who can afford to take their kids on vacation in a sagging economy?
This summer my husband, two kids, and I went on a 17-day road trip and we gave ourselves a budget of $150 a day--a total of $2,550--to cover gas, food, and lodging. We drove the length of the Mississippi River from the headwaters at Lake Itasca in northern Minnesota to the mouth in southern Louisiana, and we stayed in Best Western hotels along the way.
So, did we meet our goal? Our final total was $2,511. We were $39 under budget. But in actuality we probably came out just on target because I didn't include those few beers we drank in Memphis on my husband's birthday and I forgot to add the $6 we spent on laundry to the grand total.
How did we do it? We stuck to budget by following the rules below:
Water only. No iced tea, no apple juice, no beers, no way! At restaurants we were allowed to order water only.
Split entrees. We always started by ordering one entree for two adults and one children's meal for two kids. If we ate everything and were still hungry, we ordered more. We never wasted food.
Carry refillable water bottles. A family of four can easily spend $20 a day buying water in plastic bottles. We purchased eco-friendly Klean Kanteens, which don't leach chemicals, toxins, or funky flavors. We refilled them at hotels, restaurants, and public restrooms.
Pack snacks. We made a few grocery store runs along the way and stocked the car with dried fruit, crackers, salami, cheese, and yogurt. Sometimes we raided the snack stash for lunch.
No souvenirs over $1. We avoided stores or else we might have been tempted to buy that $40 snow globe. We kept our souvenir purchases under one dollar and collected pressed pennies (51 cents each) along the route.
Ditch the gas guzzler. Our ride was a Mercury Mariner hybrid that got 30 to 32 miles to the gallon. We figure we saved $120 by driving a fuel efficient car.
Go for hotel freebies. We bedded down at Best Westerns that offer extra value: free breakfast, Wi-Fi, and parking. We stayed in only one hotel that didn't provide breakfast, and all of our hotels were under $100 except in New Orleans where we used rewards points for a free night. It pays to be loyal to a single chain. (Be sure to take advantage of Best Western's summer promotion; stay two separate nights and get one free.)
Dive into the hotel pool. Every hotel we stayed in had a swimming pool, which offered free entertainment for the kids.
Skip admission. We often checked out a place from the outside but didn't pay to go inside. Rather than spending $30 for our family to ride the tram to the top of the Arch, we played a game of tag underneath it. Sometimes we paid for only one adult to take both kids into a museum.
Find free fun. We tracked down farmer's markets, parades, festivals, public parks.
Load your iPhone with apps. We used CheapGas to pinpoint the lowest priced gas stations and AAA Discounts to alert us of money-saving opportunities. You can download both applications for free on iTunes.

What tips and tricks do you have for traveling with kids on the cheap?