I wouldn't worry about a powder extinguisher making a mess of a cali - its your lungs you should worry about. Having been on a couple of fire training courses run by the fire brigade training centre I have actually witnessed the following:
1. Emptying a full size (i.e. the sort you see in an office) water extinguisher into a waste paper basket with lit paper has no effect other than to produce a lot of steam/smoke to disorientate you.
2. doing the same into a chip pan fire will produce a fire ball / spread of burning oil that will probably take out the adjacent pitch as well.
3. The powder extinguishers are useless, if anything comes out (the powder tends to settle & cake together) when they are set off it will be a cloud of powder that causes lung irritation with possible long term damage & have little effect on a fire.
4. A water extinguisher should not be used in a cali thats on hook up - chances are you are going to mix electrics & water.
5. A foam extinguisher is basically water + washing up liquid so marginally better but please note it usually takes 2 full size fire engines full of water to put out a car fire with professionals doing it - do you think you can do better with a tiny hand held extinguisher?
6. fire blankets are brilliant but do you know how to use one? or are you going to be looking for your reading glasses to study the instructions whilst the fire burns. I would suggest taking it out the container holding it properly & try draping it over the hob in a dry run whilst you've got a chance to do it in your own time. and as previously suggested keep it in the door pocket or the front edge of the bench somewhere that you can get it whilst you are on your way out.
7. Probably the most important thing is that a cali is replaceable you are not - even the smallest fire spend your efforts on getting every one clear as your first priority, even burning tyres explode impresively let alone a gas canister.
If you don't believe me ask a fireman what he keeps in his car / at home I would put money on the answer being just a fire blanket & possibly a CO2 extinguisher & if you get the chance to go for some "hands on" training jump at the chance. Until I did the first course I had no idea what I didn't know if that makes sense.
Andy