Lumbar support

The McKenzie book stresses the importance of good posture and good lumbar support. They sell a polyurethane lumbar role, which you place just above the beltline when you sit. This can make sitting more comfortable. There are other more low tech (and high tech) lumbar supports however, with various advantages. Here's a complete list:

1. Mckenzie Lumbar Roll Pro: strap makes it easy to carry. Made of foam that is soft and small enough that you can use it for extended periods of time without strain. Con: sometimes it is not big enough to provide sufficient support. The foam wears out after a while (expect to replace it every year).
2. Paper towel role. I prefer the smaller size that typically costs about $1. For its cost, it's actually quite effective, and since it doesn't compress as much as the McKenzie role, it can be better in some situations (such as in a car with very poor lumbar support in the seats). Be sure to keep the wrapper on so it holds together. I usually keep a spare in my car, in case I'm caught without my Mckenzie roll.
   
3. 2 pound bag of frozen peas. Aside from the fact that they melt and the bag will eventually leak, there's no better lumbar support. The peas are just right combination of cold, size, and flexibility. But, at most the bag will last an hour before it will urgently need to be put back into the freezer. I like to use these at home, such as when sitting down for a meal. You can reuse the bag if you freeze it again, but after enough reuses the peas will tend to freeze into a solid brick, which doesn't work so well. I find that the bag leaks a lot less if you wrap it in one or two plastic shopping bags.
4. Rubbermaid ice blanket ($2.50 at Target). Frozen peas are great, but they melt. The ice blanket does too, but without the mess. The package is not as flexible as a bag of peas, so it may be slightly less good ergonomically. On the other hand, having a package that lasts half a day, and doesn't need to be refrozen immediately is a big advantage. I like to combine one whole blanket with 2/3rds of a blanket, and then wrap the whole thing in about 4 plastic grocery bags, as otherwise it gets way too cold.