Can I join in? I do some of the above already.
Train the dcs to open presents carefully to save the wrapping paper and to keep it in crisp condition for future presents (no pun intended).
Ditto saving ribbons for crafts.
If you have fruit trees or have access to them, make jam during the harvest. We still have some of last year's batch of damson jam even after giving some away as presents.
Save old newspaper. They have multiple uses. We use them to put muddy boots on in the porch, scrunch and wipe windows sprayed with vinegar to get them sparkling, stick some in wet trainers to dry them quicker, protect tables when painting etc.
Save old toothbrushes for cleaning taps, difficult to reach corners, shoes. I also used some to do some stencil spray painting the other day with dd.
Bought a big bunch of coriander for just the one recipe? Save the rest by chopping it up and freezing it.
Laddered your tights? Cut off the toe bit and roll it up into a doughnut like you would for a sock bun and use it instead of a scrunchie. It's stronger than a normal hair bobble and particularly ideal if your hair is long enough to get in the way but too short for hair elastic to hold in place.
Don't use curling tongs! Use the rag curl method for tight curls or sock curl for loose curls. I used an old cut up t shirt to rag curl my hair for a 40s style hair do and it worked very well, stayed in place all day. It needs a bit of practice to not look like Shirley Temple though.
Use old mugs that have leaks as containers for random bits. My poor Denby breakfast mug had a leak but I couldn't bear to throw it out. It now holds random hair things.
Reuse old envelopes for children's dinner money, forms etc. Make your own cards and cover the writing of old envelopes with coloured paper. I sometimes do hearts or butterflies as the label.