chris.r
Reason10 nailed it quite perfectly with just Ctrl+C and Ctrl+V (no need for an extra Ctrl+D even).
Another quick way would be to hold a key and drag the right edge of a clip or selection of clips (or time selection with clips on multiple tracks?)... kind of pattern tool for the track view.
No! Duplicate is not Copy+Paste, or CTL+drag. It is one of those workflow things that are not obvious until you try for yourself. You create a bar, select it, hit CTL+D, create a variation in the copy. Select both, duplicate, you now have a four bar phrase, create variation in the last bar. Select, duplicate again, create a fill in the last bar, you have an eight bar section. Can you do it with Copy and Paste? Sure, but this is faster and even simpler.