I recommend A3 or A2 paper. The choice of weight is yours (the heavier weight the more expensive, but also easier to use when working with wet techniques).
You can use pallet watercolours or tube watercolours, Winsor and Newton make a Cotman brand which is a nice student grade.
I recommend round brushes. In terms of sizes you'll need one from the 20's, a 12, and a 7. This is again your choice; if you only buy a 12 to start you can always borrow my brushes until you know more what sizes you prefer. You'll find supplies cheapest online or you'll be able to find everything at The Range or Hobbycraft.
Paper Stretching (optional)
Bring a piece of hard board (hardware store) or a (streching board if you are at an art supply shop) if you would like to stretch your paper tits best to buy buy light weight paper.
Don't hesitate to ask any questions if you're unsure!
Oils & Acrylic
Canvas pad, canvas board or stretched canvas is fine, in a size of your choice
You need to make sure you bring black, white, red, yellow and blue, that's all you need to start with.
Bring a pack of varied sizes. If you're unsure, keep it simple and go for square flat heads. You'll find great 12 piece starter packs on Amazon for less than £5.
If you're practising at home with oils don't forget to work in a well ventilated room with white spirit on hand to clean your brushes afterwards!
I have a few full size and table top easels but its never bad thing to get one for yourself