Congratulations!
If you are planning on using reusable nappies have a look on the for sale board on here and also here and here. Reusable terry or fleece wipes will also save a fortune overthe 2 odd years our baby needs them.
Clothes are obviously a neccessity but second-hand is fine; they grow so quickly anything you buy will be in good condition. eBay obviously good for that, as are NCT sales (you don't need to be a member). At first they'll be in babygros day and night (unless there's a heatwave, in which case vests) and if you don't want these second hand the all the big supermarkets do packs of cheap ones which are absolutely fine.
Our charity shop regularly has prams and pushchairs in great condition. Personally, I couldn't have managed without a sling and you can buy second-hand here. I've never had a "changing bag", just always used a normal bag, cheaper and much nicer!chair will be ver
A bouncy will be very useful. The cheaper, light ones are better imo as they're easy to carry around and they bounce better! A babygym like this is probably not a necessity but it is a safe and entertaining place to leave your baby and once again , you can get a second-hand one, or get a friend to lend you one.
Definitely a couple of celular blankets, especially in early summer will be useful. If you co-sleep,you don't need a cot at all, though I realise that's not for everyone.
Definitely don't need a baby bath and if you get in the bath with your baby as I used to, then you don't need a support either. You certainly don't need those hooded towels, a normal one is fine and my baby was nearly a year old before I cleaned him with anything other than water so no need for "products".
Babies are actually pretty cheap but your biggest "cost" will be the loss of earnings you will suffer whilst on maternity leave if you are not lucky enough to have the kind of employer who tops this up. You would be totally amazed at how little you can live on, if you put your mind to it, so my best advice would be to cut back as much as possible now so you can get some savings behind you and also get used to living on a bit less.