We just got a water-saving shower head - it is AMAZING. I cannot do cold showers, so I collect the water from the shower in a bucket until it runs hot, and use it on my veg garden.
Buy extra mature cheddar. You need less, same price as mild.
Make sure you have decent thick curtains that cover windows. Insulation is key in winter to keeping fuel bills low. You have time to make some curtains now before cold weather comes.
Dry clothes outside whenever possible. Sunlight is the best stain remover!
Grow your hair into a style you can easily manage without styling products. And get it trimmed by a competent friend or DIY.
Keep clean colourful card and paper packing, bits of pretty coloured foil, feathers you find on walks, pieces of foam packaging (make great paint sponges). etc. Store in a large cardboard box. By the time your child is an active toddler, you will have a fabulous resource for craft activities.
Similarly, I give my kids empty packaging to play with. Kids genuinely love boxes. They also love playing with random plastic containers in the bath.
Use freecycle to ask for things you need and regularly browse what is on offer there. It is amazing how the freecycle community will come up with things you want. I'm the nicest possible way, if there is a "posh" area near you, join that freecycle (assuming you have access to a car). It is worth driving 5 minutes further and honestly, rich people give away better quality stuff and give away a lot more as they often replace things that aren't knackered. Good quality curtains, furniture, kitchen or garden equipment, etc. Typically if I get something nice I try and leave a little gift like a pot of homegrown herbs or flowers. Freecyclers love that.
When buying Used on Ebay plan ahead. Eg Don't be looking for a kids snowsuit in late November - the auctions will drive the price up. Anticipate the fact that your child will grow, and buy out of season. I got some insanely cheap good quality bundles for my kids this way!
Know what things are worth. I just bought 344 Megabloks from a guy nearby who was moving house, for £10. No child needs 344 Megabloks! I'm going to sell half and keep half. I expect to easily sell 150 Megabloks for £10 so I've spent nothing.
If you have a garden, look out for people giving away seedlings surplus to requirements. I got a raspberry cane this way- in year 1 I had 1 raspberry! Now I have a whole patch of them, the damned things pop up all over. We have raspberries to spare, I freeze some and also share with my neighbours and they reciprocate with surplus runner beans.
Go blackberry picking in late summer, there are bound to be some brambles nearby. Just take some, leave the rest for the birds.