I've been doing this so long, I forgot that I do it. So what's a multi-tasking product? One that has multiple uses in your preparedness supplies, of course, to reduce cost and storage space without losing capability. For your GO bag, it can also lighten your weight. The obvious item is salt. It can be used for flavoring and many medicinal uses. In larger volumes and with some expertise, it can be used for food preservation.
What are some less obvious multi-taskers? My favorite is alcohol gel hand sanitizer. Most of these gels have between 60% and 75% alcohol so they are flammable within warmer temperature regions. They can also be used, VERY CAREFULLY, as fire-starter. A small squirt on a piece of cotton, fabric scrap or small ball of dryer lint can help start other tinder or kindling. It is not as effective in very cold temps (near or below freezing) but can be a lifesaver in damp conditions. I just found the 72% in 10 foil pouches at CVS for $1.99. That will help get around the potential leaking bottle issue.
Candles are another multi-tasker. By selecting your candles carefully for composition and size, you may be able to harness them for both light and as back-up cooking fuel. A short multi-wicked canned candle is more likely to be a multi-tasker, and beeswax a better choice than miscellaneous waxes. These may not cook a raw piece of meat, but may be enough to warm water to warm you up. Short thin candle ends or small pieces with a wick can be harnessed in the fire-starter arena if needed. By pullin a piece of string or thread across a candle a few times, you can coat it in wax and make it more waterproof and easier to use -- especially thread. Waxing it makes it tangle and knot-up less when you sew.
I'm a big fan of net fabric, by the yard, from Walmart or fabric store. It comes in several mesh densities and a few colors. We don't have no-see-ums here, so I get the slightly larger mesh. Yardage is about 55 inches wide and can be used as-is with a little help from a walking stick or piece of string for a bug net over a sleeping bag or 'screen door' on a make-shift shelter. With a bit more work, it can become a net around your hat to exclude bugs -- up to sewing some as a tube and putting a simple draw-string on top and bottom. I keep 3 yards of this, in one piece, in both my Emergency first aid kit and my GO bag. One piece is black and the other is a bronzy medium brown.
So what are your favorite multi-tasking items?