Happy Birthday! What a nice gift!
I'm going to suggest the obvious from Amazon... some books to help you improve your photography.
I don't know what level you're at, but Bryan Peterson has written some excellent books that are great for beginner through what I'd consider serious intermediate level. They're very easy to read and assume no prior knowledge, but manage to avoid talking down to readers who might already know some of what's presented.
A book I think every photographer should own, read, practice and re-read on occasion, is:
Understanding Exposure (4th Edition)
If you'd like to improve your "photographer's eye" and compositional skills, this one is excellent:
Understanding Composition (Field Guide)
And, finally, if you're interested in flash photography but don't fully understand how to use and control a flash gun properly, try this:
Understanding Flash Photography
I have all three and re-read them from time-to-time, as they're genuinely enjoyable books with plenty of sound advice and information. If you read and learn everything in any one of these books, you'll have a very solid understanding of the subject matter. Read them all, and you'll have a far better grasp of photography fundamentals - technical and artistic - than many folks in forums such as these.
At current Amazon UK prices, you'd get all three for around £55 in total, so you'd have to contribute a fiver on top of your gift card. Well worth it, though