For my Nexus 7 I use this Motorola bluetooth keyboard with trackpad
. That works very well. Even my wife who types very fast has no trouble dealing with it. But as the others have said, it is another piece of gear to lug around.
I see the main advantage of a tablet in the many useful apps that are available. E.g. the navigation apps and VOIP apps (free calls) are very good and very useful. For little money I even bought a very good office app from Kingsoft. But I hardly ever use it. The screen is just too small.
The other use of the tablet is to carry picture and video files around. Music files are also possible, but for a reasonable listening quality you need good earphones. I have a Sony set - another piece of gear to lug.
At the end of the day, it is probably more practical to carry a small (e.g. 13") laptop around. Unfortunately those are a lot more expensive than my 32GB Nexus 7 for which I paid $230.