A wide angle lens is a must (your 28-80 should be ok... but if there's any way you can stretch to something that goes down to 24mm then go for it

), plus a telephoto if you have one - 75-300mm or something similar will let you zoom in and isolate aspects of the landscape, as well as compress perspective for things like lines of trees, or the receding shapes of the crags the Wall is built on.
Filters - ND grads, polariser and warm-up (81b).
Film - Velvia 50 every time for me, but then I suppose its entirely personal... I love to get some movement in my shots - long grass blowing in the wind, clouds racing across the sky, rushing water turned to mist - so the slow speed is ideal. I think the colours and saturation etc are pretty similar, so you might want to go for the 100 ISO to give you a bit more versatility. Also consider some black & white shots - maybe a few rolls of fast film for grainy, atmospheric images.
Your tripod should be as sturdy as possible - in general the heavier the better, but as you'll be walking, weight will be an issue...
A couple of locations to look out for when you're on the Wall include: Sycamore Gap (made famous by Kevin Costner in Robin Hood, Prince of Thieves), Steel Rigg, and Crag Lough... do a Google Image Search on these for an idea of what to expect.