I may see you there. I too am in wave 2 corral 1. 2017 was my first year at Boston. There were various chews, bars, water, Gatoraid, bananas, and other items available to runners at the village. If taking BAA buses the ride is about an hour long. So you may only want to take food with you that you want to consume before you arrive at the runner village/middle school. I arrived early at the village and was probably on one of the first 20 buses to drop off runners. I was in the first wave last year. I got in line for the portable toilets about every 20 to 30 minutes regardless of whether or not I felt I had to go as the lines got 2 to 4 times longer each time. When I arrived they may have been some unoccupied toilets. But within say 15 to 20 minutes the line was maybe 5 to 10 runners deep and much longer each time I went. By the time it was close for the first wave to be called to assemble in the parking lot at the village/middle school I may have gotten back in line very shortly after exiting one. Some runners urinated along what may have been a fence in the parking lot with some shrubs are trees but I don't think that was necessary. There are portable tolets in the parking lot at the CVS just before the starting line corrals one may use. I would use these toilets or a wide mouth bottle in that parking lot as the last oportunity before the start. There were about 10 runners near me who urinated along the course not far from the start where there were fewer bystanders.
The first collection of clothing is in the parking lot at the middle school. If one thinks they may want to hold onto clothing longer to stay warm or dry then they have plenty of oportunities to get rid of it all along the long walk from the middle schoool one's corral. There are volunteers with large bags all along the walk collecting clothing and trash.
I found it easy to urinate in a large mouth Gatorade bottle near the corrals at Chicago by putting the bottle down my roomy sweat pants. I did not take a garbage bag to either race last year but plan to this year.
The first aid station is not far from the parking lot stagging area at Boston. It had sun screen for runners. I also saw a dispensor or two in the parking lot or just past it on the walk to the corrals. I think Band-Aids were also available at the first aid station for those who needed them for their nipples or other areas.
Don't forget to show your bid to the volunteers when you enter the parking lot of the middle school for the walk to the corrals and when you enter your corral if you have clothing that is covering it.