This is one of those tips that saves chiefly on aggravation and time, but can also save money.
Have spares on hand.
What are the things you run out of and routinely need to replace? Pens, batteries, razor blades, tissues, paper towels, garbage bags, kitty litter, batteries, hand lotion, toothpaste, toothbrushes, dental floss, sunblock, tape, envelopes, paper, labels, stationery, recordable CDs, light bulbs, printer toner or ink?
These sorts of things are often loss leaders and many of them can be bought in bulk. In some cases, you'll find that ten times the quantity only costs three times as much. And even when there aren't crazy bulk discounts to be had, by planning ahead you'll have the opportunity to look for a good price. If you wait till it's an emergency, you'll end up stuck with whatever price you see first.
And, best, when you need something, it's not a crisis. You'll have planned ahead. Preventable crises? They should be prevented.
If you have a tiny home, it may be unfeasible to stock up on many of these things, but if you have the space, it's a great way to save money and peace of mind. Jen and I are still working our way through a case (ten reams) of paper I bought years before we met. We're still using the dental floss of which we bought every pack we could when it was on sale as a loss leader. On lots of occasions when my bike's needed maintenance, I've been back riding faster than I would have because I had the parts on hand.
Can you set aside a day to note what spares you need, and either get them or make a note to look for them when the price is right?