I just have one "Singleton" project that collects my singleton actions. Even a lot of my "single action" actions wind up in large organizational projects. For instance, the aforementioned "call for haircut" action would wind up in my "Personal Maintenance" project (non-sequential, made up of a lot sub-projects (action groups)) as would "iron shirts". "Subscribe to journal" would end up in my "Professional Development" project.
I organize most of my actions into large super-projects that roughly coincide to specific long-term goals in my life. "Professional Development" is actually called "Practice Design" in my case and includes things like "sketch daily" (an action), "take advanced rendering course" (a sub project) and "subscribe to new design magazine" (also a sub-project). Each of my topmost projects (except for "Singletons") represents a specific life goal and then all of my actual projects (like "complete client project" or "write research paper for art history") is filed as an action group under those larger projects (or under another action group under those projects -- the hierarchy rarely gets more than two action groups deep though sometimes it edges up to three).
This way, I have some notion of my progress toward my overall life goals just by looking at what's been getting done in each super-project and, more importantly, every task I add to my action list is organized in terms of how it advances those goals. If a task doesn't fit into one of my major super-projects, I often decide just to abandon it right there since it doesn't actually serve any of my personal goals. Sometimes, I'll collect these "unfiled" tasks and projects in a someday/maybe file (separate from OF, I use VoodooPad for someday/maybe among other tasks) that I consult during my 30,000-50,000+ ft. reviews to determine if I might need to consider some new life goals or if could better structure my super-projects to reflect my life goals.
Consequently, I have very few actual singleton actions -- usually zero or one, rarely more than three.