Potential Officer Visits are arranged via the Area Careers Liaison Officer (ACLO) not your local Armed Forces Careers Office (AFCO). As clearly suggested they are the people to talk to as no one has a clue which type of POV you are on and they all differ. You could just be accommodated at Raleigh and visiting a Ship at Devonport, for example.
You ACLO should brief you on the acquaint visit, kit to take, transport arrangements and give an overview of the acquaint.
It's aimed to give an insight into the branch you wish to join and will doubtless include a visit to items of interest at HMS Raleigh if that's where the POV is centred, such as the Submarine School, Fire School, Damage Repair Instruction Unit, Logistics School and possibly an introduction to the gym and swimming pool, not to mention the possibility of visiting the Harbour Training Ship, Jupiter Point and maybe a trip in a Pacific RIB or similar.
Short of a formal kitlist being issued, if you are going for three days, you will probably need washgear, towel, flipflops, swimwear, sportskit and trainers. You'll need about three civilian shirts, five changes of socks/underwear, a warm civilian coat.
You'll be expected to wear suit/shirt/ties/shoes for most of the time but stuff like overalls, boots, combats etc will be loaned if required (if you end up doing the assault course/high obstacle course, etc).