I always like having my own Pooleys, but it depends how much flying to different airfields you do. Depending on budget, cheap GPS for airspace awareness is always useful. None of these are probably that useful until after your PPL.
Do you have a kneeboard? A definite must have. Half mil chart with pens and erasers? Good pair of sunglasses?
If you intend to fly in the cooler months, a carbon monoxide detector can put your mind at rest when using the heaters. You can get really good electric ones (like a smoke alarm) for £20, or the little plastic stick on ones (not great if you won't be flying the same aircraft).