While there is a question about sharpening a knife in the wild, I have a different issue. We are in the midst of moving house, so my honing iron is packed away in a box god knows where.
I have a blunt knife, how can I sharpen it?
One way is using the bottom of a ceramic plate or cup.
On the bottom of some of these, you'll find unglazed ceramic where it's been cut, using this you can rub the blade of the knife along this unglazed edge, and because it's harder than the material of most knives (not hardened steel maybe) it will cause the edge of the knife to align, the same way a toning rod does.
A toning rod works because it's harder than the material it's toning, causing the material's atoms to align and eventually getting rid of microscopic dents and edges which gives the knife the most perfect possible edge for cutting.
Due to this, you can actually use another knife to sharpen one, if you carefully use the back of your knife, and run the knife to be sharpened up and down it, pulling towards you at an angle of about 45 degrees.
If you have high grit sandpaper you can use that to sharpen your knife. Wrap it around something hard (tile/brick) and you can make a makeshift blade sharpener.
You can use a leather belt. Put some water on the belt and sharpen the knife on the "soft" side (the side facing towards your body when you wear it.)
You may be able to sharpen the blade by using a brick or stone as a whetstone.
You can use a steel rod. My family always keeps one aout of a box when we are moving(aka every 2 years). How you do that is you take out a steel rod( should have a meatel, thick stick and a heavy duty plastic handle) take the dull knife and at a slight angle drag it aross the meatal part. Doing that miltiple times at a kind of fast speed will sharpen your knife.
A piece of cardboard can be used to sharpen a knife, especially if the knife isn't extremely dull and just needs that final touch to give it a razor's edge.
Just sharpen the blade on the edge of the piece of cardboard as you would if you were using any other material. Run the entire edge against the edge of the cardboard on both sides.
It is difficult to verbalize exactly how to do this without showing an example, so I found a useful YouTube video HERE.