Sallyc,
http://forum.justyou.co.uk/thread-80080.html
Even though there are political relaxations between the USA & Cuba re the embargo I am guessing that the supply of what we may think of as basic needs has not filtered down to the shop shelves in Cuba. If you think you may need it - especially medication, batteries etc then take them with you.
As regards the Visa this was always in the past referred to as a tourist card and it was stamped at immigration with part of the card retained by you to be surrendered on departure. Only the card was stamped and there was thus no stamp on the passport and no evidence on the passport that you had been to Cuba. This was of particular interest to travellers to the USA who might have thought that a Cuba stamp may hinder progress at USA immigration.
However, should you want a stamp, then Cuban immigration are usually quite happy to do this, but you need to ask. I have done this twice over the years - but on passports that were shortly due for renewal! At your own risk!. The last time the girl on immigration even agreed with me the place the passport be stamped.
As for dressing up in the evenings Cuba is fairly casual but you could "go posh" most evenings if you wanted to.
Enjoy, Ian.