All great suggestions here - the one additional thing I'll mention as I don't think anyone has yet is to get very, very comfortable (if you're not already) with fixing the most likely things that can go wrong while you're out on the road. It's one thing for your friends to help you with these adjustments, but if you can you should pick up/borrow a copy of a reference bike mechanic's book like Zinn ($25 well spent) and practice the following:
- changing a flat tire (practice getting a tire off and tube out 10-15 times in front of the TV before you leave and you'll be glad you did when you flat on a rainy dark night) Also bring along a decent patch kit with NEW cement (and not a glueless patch kit) before you leave and you can re-use tubes as needed rather than buying new ones. (glueless patch kits are light and great and I always carry one around myself but the tube is basically garbage after being fixed once... not so great for touring on the cheap)
- minor gear adjustments: deliberately screw up your front and rear derailleur adjustments a few times and then dial it back in until you can do this by feel
- minor brake adjustments
- regular chain lubing/wiping (a small bottle of ProLink will also be $5-6 well spent on a 1600 km+ tour)
- at least read over the steps for basic wheel truing, spoke repair/replacement before you leave and carry a spoke tool if you can
Other very small things based on my own experience:
- you can get away with 1x pair of bike shorts if you're doing this on the cheap, but I really would recommend not completing 100 km+ days in regular street shorts/pants. You can dry shorts out for the next day by rolling them in a towel a couple of times and then hanging. Same goes for a jersey - 1x should be fine but a cotton shirt will be miserable on a warmer or rainy day
- +1 on the suggestion of putting a bit of cash aside for motel stays a few times throughout the trip. This can make a huge difference to your outlook (and sanity) during those rainy dark nights
- if you can, setting aside $20-30 to have your road bike properly fitted at a LBS may be money well spent up front. (they may even do this for free if you're buying some of the above supplies there) A bar or seat position that is off may go unnoticed on your shorter rides, but may cause you nothing but grief during those 3+ hr days