Barring taking a helmet on a 50-mile ride before buying it:
Some kinds of chin straps, for example, won't stay tight, and some kinds of cages aren't comfortable no matter how I adjust them. What should I look for?
This isn't a product recommendation question (although that would be nice). I'm interested in knowing what features to look for.
Alternately, is there anything I can do to an existing helmet to make it more comfortable on longer rides?
(If it'll help, I ride for commuting, running errands, and touring; aero or ultra-light features are appreciated but aren't a priority, but ventilation is important.)