You definitely won't ever have to wear a collared shirt as a loader. You've taken a grunt job that's out of public sight so appearance is a very low priority and a dress code other than safety things like good work boots basically doesn't exist.
For your first week where you are partly in training class, partly loading, wear a tshirt that's in decent shape but not one you really care about since it will get at least a little dirty if you're loader material, and getting torn is always a possibility.
You are right, its going to be hot. Once you're outta training class and working for hours in the heat, look at what other guys who care little about what they look like and a lot about being good (fast) and even a little comfortable or sometimes just survive come to work wearing. Some loaders and unloaders have become very clean cut by wearing old worn cut up tshirts. Those rags, um, I mean tshirts sometimes hardly cover anything, but when time is ticking away and there seems to be more cardboard anyplace other than in the trailers where it belongs, most sups I have found would definitely rather have a working, faster loader who's hardly wearing anything above the top of his boxers, than a slower loader, who might even be recovering in the a/c office from the heat, or called in sick and totally absent for the day.
