For us, the first 1.5 days or so is all about the rules. We spend most of kickoff just digesting the rules and then analyze what we think are the most valuable aspects of the game from a rules perspective. By the end of Sunday we have a ranked list of all the tasks in the game. We then spend most of the week prototyping, prototyping, prototyping, prototyping. (By the way you should really prototype during week 1 if I wasn't clear before.
) But seriously, prototyping is super important. By the end of week one we have a general idea of all of the mechanisms on the robot and spend the next few weeks refining the robot. So, this year for example, we were pretty sure that we were going to have a wheeled shooter on a tank drive chassis with pneumatic wheels and some sort of intake by the second Saturday. At this point we will also seriously start to CAD.
We also spend some time (this year A LOT of time) on building field elements during the first week. We also usually make sure to order a few things that we know we will need/will sell out quickly/game pieces early in the week, so we don't have to worry about it later and risk long lead times.