Jim: In January 2004, I looked up the various MLB teams' preliminary schedules on their web sites and depicted the results on what turned out to be several sheets of graph paper taped together. Figuring the month April might be a little chilly for a road trip around the Midwest and Northeast, I started with the first weekend of May (actually, Friday, April 30) and went all the way to the end of the season, charting the teams that were within reasonable driving distance of Chicago. "M" indicates Mondays, although it soon became apparent that it was easy to tell which days were Mondays, because they had fewer games than any other day of the week. May 31 has a red "M" to indicate it's a holiday. Home games for each team are indicated by a horizontal line for each game: blue (night game), red (day game), or gray (unknown, because some teams didn't have game times posted in January, when I made the chart). The teams are numbered so I could more easily follow them all the way across.
Then using the chart together with the "driving times" figures from a road atlas, I tried to come up with itineraries that would involve 10 or 11 games, in consecutive cities that were "next to" each other that didn't involve too much driving in between, and ideally involving stops in Montreal, Boston, and Pittsburgh, the three cities Levi and I agreed that we especially wanted to see games in.
I managed to come up with four potential itineraries, and Levi chose the one that he liked best, which happened to be the only one with St. Louis Cardinals games.
From then on, the web site of the Automobile Club of Southern California (AAA) was the planning tool I used, mainly because I wanted to have our reservations set in advance. I was most happy with the motel I found in Boston, relatively cheap because it wasn't downtown, but still ideally located for taking the trolley to Fenway Park.
The main impetus for renting a car for the trip was the fact that Levi doesn't have one of his own, but I have to say, it was very nice to be driving an essentially brand-new car around for two weeks, and I assume the hangers-on who joined us for parts of the trip and ended up riding in the back seat liked the fact that it was a big American car. (When we had to fill the gas tank, our wallets liked the fact that it was only a car and not an SUV.)
I bought tickets for two of the games as soon as possible after they went on sale during the winter. I figured the Red Sox game at Fenway Park would sell out quickly (it did), and I figured the Phillies game in their new stadium might sell out before our trip started (it didn't, but it was close). Levi bought tickets for the Cardinals in advance once we figured out how many people were going to join us for that game. I ended up buying Brewers tickets a couple of weeks before the trip when I discovered their "family pack" deal was going to apply to the game we were seeing and we could get a big discount. Finally, I bought someone's Tigers season tickets on eBay shortly before the trip, which was the only good deal I found on eBay after checking occasionally during the months prior to the trip.
Three changes were made to the itinerary before we actually set out on the trip. First, it had originally started with a Sunday afternoon game in St. Louis. I realized it made much more sense to start the trip on a Saturday, started looking at minor-league schedules, and came up with a Class A game in Davenport, Iowa.
Much later, I had realized that I had somehow passed over the fact that the Chicago White Sox were playing at home that weekend, and we could have either extended the trip to include Friday, or seen the Sox Saturday night instead of the minor-league game. But, as it turned out, we got to see the White Sox anyway. They had to make up an interleague game with the Phillies, and the makeup game was neatly scheduled into our itinerary as an afternoon game on the day we'd be back in Chicago, heading for Milwaukee to see a night game there, thus allowing us to see two games in one day.
The third change was the result of the Fox network exercising its prerogative to mess around with games' start times and switching the Pirates' Saturday night game to an afternoon game. The main effect of this was forcing us to drive a third of the way across Pennsylvania immediately after the Phillies' Friday night game and spend an extra night in a motel (instead of enjoying the hospitality of my relatives in the Philadelphia suburbs).
Oh, and I bought several boxes of Hostess Baseballs (perpetually on sale at my local Ralphs at 2 for $5.00).