I take it you mean Phase One Alpha rather than CMS(R) which is a 2 week course run at the end of basic training. This will be your first w/e then which will probably be a your TAC or another within the Regt/Bn, this will be a fairly casual affair as you probably haven't even got your uniform yet, so can't do much. Many units use this w/e as a method of selection, so be careful and don't kick the arrse out ot it.
Kit, those this mentioned previously are fine, I would also bring sports kit as there should be a run or similar added, or even a sports activity. Bring money for the bar, essential.
Is siggy a nick name or TA career choice ? If you are in a *ahem* proper Regt and coming to play down on the south coast this w/e I might see you there, I'll be the old fart with the very shiny boots
Lots of induction training, how to iron your kit, march in a straight line, salute the ones that don't do any real work etc. Sports kit is a good idea as you may do a PFT (1 and half mile run, sit ups and press ups) so be carefull not to overdo the Friday night bar sketch!!
Enthusiasm is the most important thing that they look for in a new recruit, hopefully everything else will fall into place as the training progresses. The 'old git' in shiny boots will accept that it is your first time in green and will give loads of advice on what to bring on the next weekend so listen very very carefully as he may only say it once.