The file on a P4 is great for making shavings from a magnesium block. Just tried it. Less than a minute of work and I had a dime sized pile.

I do love my Wave.

I carry a diamond-sharpening card in my wallet behind a business card to protect the wallet and the card. It does double duty keeping an edge on my knives and seems to file down anything that needs it. A piece of wet and dry sand paper folded up could stand in as a compact way to smooth many things up. Ragweed Forge carries the credit card sized diamond-sharpening card

And then there is alwas the Micra...