Custom t-shirts can give team members a unique gift at the end of the team day. It could be worth including on the t-shirt the names of those attending the team day as a reminder of those who attended. It could also be nice to include a timetable of the day on the t-shirt, particularly if the events of the day are especially memorable or unusual. Alternatively, it is often striking to keep it simple; maybe even use just one phrase to sum up the day.
It is very simple to organise and order a large number of t-shirts, and many manufacturers are able to cater for large orders. When ordering t-shirts for the team, it could be worth asking for their sizes prior to ordering, to ensure that the t-shirts provided fit them and look smart. Alternatively, it is often worth ordering larger sizes to accommodate the whole team. Smaller members of the team could pull their custom t-shirts in, if required, by wearing a belt or by tucking it into their trousers or skirt. It is also worth ordering several extra custom t-shirts just in case as accidents do happen.