I take it your looking for a backpack to do multiday trips?
You can pick up a good enough pack for about £50, I'd pop to your local outdoors shop and try a few on.
Similarly you need to buy the boots that fit the best - whether they are the £50 or £150 ones. However, you get what you pay for. I have odd narrow feet with funny heals and bots is a real problem for me. My £30 ones out of the local surplus were comfy as, and did the job for a year, but the soles are worn down and they are in a nick (a bad one - still live in the boot of the car as backups). My new (well 2 years old) leather scarpa rangers are a slight compromise on comfort, but will last for years if treated well. Its taken me ages to break them in, and they still rub on ascents, which is far from ideal.
Tent, Id go with this - light, cheap and just for you!
http://www.amazon.co.uk/dp/B00322QR...de=asn&creative=22218&creativeASIN=B00322QRQE
Just got one myself, but havent tried it out yet
With £50 on a pack, £40 on a tent, this leaves you with £110 to get some good quality boots when you find the ones that are right for you.
You already kitted out with a mat and a sleeping bag? If not simple foam mat, cheap as chips, and try tesco for a down bag - not great, but cheap and will tide you over till you get something better. In fact, mine is still my regular summer bag after 3 years!
Welcome to the forum, and to a very rewarding hobby! Enjoy.