As it's in the Autumn I'd suggest adding a bivvy bag (waterproof gore-tex/canvas outer layer for sleeping bags):
I'd also put together a basha kit (waterproof poncho/tarpaulin in the appropriate camo, 2x bungee cords, 2x tent pegs and a roll of 'green hairy' string). My personal one is packed for the Reading festival this weekend so I can't demo how one can be put up, however here's an idea:
The standard format is like this; one end is pinned down by tent pegs while the other is held up by bungees wrapped around trees/hedges/fences etc. They can be tensioned by using string attached to a poncho's hood/tarp's centre webbing straps. In the daytime you'll want to take it down completely if the weather's ok, but if it's pouring it down just lower the basha on it's bungees until it touches your bergan and covers your sleeping kit completely.
You can also run a line of string between 2 trees and peg the basha down at all four corners with the string holding the centre line up. This is referred to as an 'officer's basha' and it means you need to carry more tent pegs- also more difficult to get in and out of if you're attacked in the night and you need to stand to.
If you've already decided to take a small tent then disregard this, however buying all the fixings for a basha usually works out cheaper than buying a decent 1-2 man tent. Basha kits are pretty lightweight too and take up much less room when packed up, mine is roughly 15-20cm by 12cm, 4cm thick in it's stuff sack. Most new basha tarps/ponchos will come in a little stuff sack which you can fit the pegs, string and bungees into easily.
Aside from that just take all of the kit Aengus has mentioned, some real no-brainer stuff on there which is difficult to forget.