As someone said clean pants are the order of the day.
The only things they seem to care about is.
a. Have you paid
b. Do you have your passport with you.
Then its kit off and round the stations
And after its all finished they do have a shower for the use of.
During the Brain activity test thingy (which is the most horrible test in the whole lot) they draw on your head and use a gel with what feels like sand through it to make the contacts with the electrodes. Much better to get it all away so your not scratching your head all day.
If it helps i went in Chinos and Causal shirt and shoes.
Good luck
MJ