My preference is to keep the cluster to a minimum, and you could do this by thinking about what you already have racked. You really only need a few items to get the job done.
As an example, I keep my chalk bag attached to me by 6mm acc. cord that I can use for a prusik, if need be. I have another prusik stuck on a carabiner that I use as my third hand/rappel backup. For the climbing I do, I don't have any devices that I bring along for just in case.
Now, if you are talking about big walls and jugging up them... a dedicated device would be more efficient. Someone else can pick up the conversation here, but there are loads of posts and articles explaining the how, what, when, and where.
Edit to add: csproul's response below is a perfect example of using the tools you already have available.
Think about the possibility of you leaving those dedicated devices in your pack when already on a climb - what are you to do then?
anyone do this? or do you just randomly rack all the tools you use for this purpose amongst your climbing pro?
When I'm free climbing, I always have a couple of slings and a/or a belay device on me whether I'm leading or following. That's all that's need to ascend a rope should I have to. Why would you need a separate "bag" of stuff?
When I'm aiding, I usually have a pair of ascenders, or at least a Grigri and something else.
csproul From Davis, CA Joined Dec 3, 2009 355 points