Any bags, wallets, pens, keys etc. will have to be placed in a locker that they have. The only thing you have on you is the locker key and your ID (as tropicalwind mentioned).
As for calculators, you won't need one. The real DAT has problems set up so everything can be done in your head. There might be one problem that requires you to long division, however I think that I was doing long division because I didn't approach the problem intelligently. I think that you practice well you should be able to do all the calculations in your head.
I say this because if you practice well, your estimation skills will be so good that you can rule out three answer choices after doing a couple of seconds of mental acrobatics.
Also, by doing things in your head I don't mean that you shouldn't use the scratch paper. The paper is very useful to write intermediate results and mostly important to draw diagrams and to help you organize problems in your head.
One thing I did during my 15 minute break was to write down a trigonometry table. Which means to write down the sides you use to determine sin, tan and cos and their reciprocals cosec, cot and sec. Even more useful is to write down a table of the values for 0, 30, 60 and 90 degrees for all those functions. Do this during break so your head will be focused on computation instead of recall. Mixing up computation and recall during a stressful test can lead to bad things IMHO. You don't want to get half way through a problem while wondering if you remembered the right value for cosec 30.
You can write down other stuff like probability formulas if you wish.