You won't get any amenity kit on the day time flight, and my experience on the night flights is it is pretty woeful. So take a good eye mask, good headphones (obviously noise cancelling is best) or ear plugs if you want to try to sleep, a head/neck pillow and warm clothing in layers in case the cabin is either freezing or boiling, or in many cases both at different times of the journey!
Honestly T5 is fine without status, there are plenty of places to get reasonable food and a beer before takeoff. I would highly advise you take an empty water bottle through security and fill it up, or buy water at one of the shops. I don't know what the current policy is because it keeps changing, but BA in the past have refused to give out bottles of water and only provide very small (maybe 150 ml) plastic glasses.