It would be helpful to be able to create "issue carts". An issue cart would be able to contain specific issues rather than just search parameters. This solves a problem that cannot currently be solved with subtasks or versions.

Take, for example, a developer who has 30 issues assigned to him. Out of those 30, he plans to work on a group of five issues first, a group of ten next, and the remaining issues last. The five first issues could be put in one cart, the ten issues in another, and the remaining fifteen in another cart. An issue cart would be the best way to handle this since the issues aren't related by context or by release version.

It is also useful since carts would be able to be private rather than affecting the issues for everyone, as relating or versioning issues will. This way, a person can have a private way of grouping issues. Ideally, a cart would be able to be shared like a filter.