DH's old sweatshirts, his shirts that are worn, old sheets or pillowcases, scraps of batting from another project. Anything that is about the same thickness as your quilt sandwich will be

Thanks for all the great ideas! I know I need to practice, but I keep making more 'real ones' and never get to the practice pieces and then I'm not happy with the results. Go figure!!!

I also use my practice sandwiches over and over - different color threads. In the end they are used for batting/insulation pieces in potholders.

I hit the yard sales every year for quilting supplies. I get lots of usable items, for batting, like bed liners, bedspreads, the kind that has a light batting on the backs of them. These you can also use as practice quilting. I also go for used blankets & sheets. You will be surprised what you can find at yard sales. Last week I found a king sized batting for $1.00 & 10 yards of fabric for $6.00. You can also ask all your friends & family for all their clothing they are getting rid of. I make memory quilts out of clothing for people & they love them. Clothing works great & really helps with the cost of things.

I have basenjis, and they tend to tear up their bedding - every time. I found that Walmart sells a blanket that is more like felt, not woven, so the dogs can rip it up without threads being there to cause trouble.
So one day I thought I'd cover what they had because they looked like swiss cheese. I just covered it with another layer on each side, of the same blanket, so that's 3 layers.
I used them for FMQ practice, and it seemed to work fine

As much as I HATE WAL-MART, they use to have a $1 table of materials that didn't sell. Bet you would find something there to practice on. I also use a flannel for batting in my table runners, maybe you will find some old flannel pjs at the good will stores.

Lots of great ideas here! Also keep you practice squares uniform in size. Then QAYG them together to make a quilt sampler.

I headed back into the city today, armed with the suggestions in this thread, thank you very much ladies!

At the reuse center, I found a twin sheet, baby blue, that I can use for fabric, and one piece of what looks like it might be a muslin, about a 1/4 yard. Plus an armload of other things I might use one day.

I hit one of the few independent fabric shops in town, and .... found muslin for inexpensive. Yay!! $7.99/M (39") - BUT, it's 114" wide, so it works out to nearly US pricing. :) I picked up 3 meters. (I love how the widths are always listed in inches, but we buy in meters. )

Then we headed to Ikea, about an hour away from us, so I grabbed a half dozen of the $3 throws.

The two of those things should keep me in practice pads for quite some time, especially if I use the dissolving thread too.

I really like the idea of using these to make a QAYG too,... I will try to keep them uniform, and save the best ones. The ones with multiple pillar crashes may become dog beds and pot holders (it's just, eventually, you don't need any more pot holders.). :)

I'm really looking forward to the weather clearing up, we went right from snow to April showers all through May and this part of June so far, so I can hit some more garage / yard sales. I have made some pretty good scores at those sorts of sales.

Our walmarts here don't sell fabric, haven't in quite a few years, so there's no clearance table for us. We do from time to time take vacation in the US, so I will remember to check them out when we're there. :)

The felt is a great idea too. I run into it from time to time at the thrift store.

Our quilt guild makes charity quilts, and they give me free rein to practice my machine quilting. The guild provides fabric and batting, so it's a good way to get the practice I need.

The guild I joined a couple of months ago doesn't really have a lot of that going on yet, but there are a few others around here, maybe I will see if I can find one who needs that sort of help.

In the meantime, what's a good size for the practice pads if I want to use them for QAYG eventually? the least wasteful size looks like about 16x20, but that seems big for a quilt block, so I'd like to hear suggestions. :)