Great article over at the ubiquitous Dieline called the Top 15 Fonts for Packaging Design. Lot's of great stuff in it - it really is a must read.Some highlights:
Keep # of Fonts to a Minimum. Try to keep the number of fonts on a package at 2-3 typefaces total. It's best to keep the number of fonts used in a design to a minimum. Sometimes there are exceptions, but use your best judgment.
Kerning is Mandatory. No font, no matter how expensive or good it is, is immune to irregular kerning. You should always double-check the spacing between letters to make sure they're even. This will make the difference between amateur design and professional work.
Fonts are Not Infallible. If a specific letter looks weird or somehow 'off', use your judgment to repair or replace it. Some fonts (especially hand-written scripts and free fonts) have strange-looking characters. You should use a critical eye and replace or tweak a character until it looks right.
Readability is King. If you can't read it, it probably doesn't belong on packaging. Again, there are exceptions to this rule, but it's rare. No matter how 'cool' a font is, if you can't read it, the package is handicapped in conveying its message - what's inside and why you should buy it.
Sound advice for all!
