I will chime in to say that whilst the book of Gray's Anatomy for Students hasn't been very useful, I have found the online subscription it comes with to be useful indeed. In both surface anatomy classes and dissection, having Gray's on hand was a very good way of making sense of what we were actually doing - because it is all explained. But I appreciate that this only worked well because the sessions were structured in a way that we could read Gray's on iPads etc. - so your experiences will inevitably differ.
Overall, you shouldn't buy any textbooks for medical school before you arrive. There's no point. Your lectures may be fantastic, or they may not be. The lecture notes faculty provides might be fantastic, or they might not. The notes you get from your peers may be fantastic, or they might not. You just won't know.
But my advice is that once you arrive - don't be afraid to explore the books in the libraries. If you think they're useful, then buy them. Ultimately, it's your learning and if you see something you think could help with that, then it makes sense to buy one.