This is an idea for a new feature, not a critical thing but it would be very handy.
It'd be great to be able to associate a list of checkable items to an issue. It is quite common to find a case where a particular issue involves more than one steps. These steps are too small and not independent, so they cannot be issues.
If, given an issue, I could maintain a list of TODO items (that I can add, delete, check and uncheck) then it would be easy to keep track on progress, changes on scope, etc...
I found that most engineers, even those that use JIRA intensively, also keep a TODO list on a text file, Outlook Tasks or a piece of paper. It'd be great to integrate these two kinds of granularity in JIRA.
I'd really love to see this one implemented.