What's your budget? Diamond cards like ez-lap are good for about $20. They're compact and you use them like a regular stone. Usually for a set of three different grits. Fallkniven makes a diamond on one side ceramic on the other medium/fine sharpener for $20-30 depending on where you find them. They're heavier, but high quality and I like the one I have.
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A gentleman should always be able to break his fast in the manner of a gentleman where so ever he may find himself.--Good Omens