I do that too and, for me, the trick is to complete the Clarify step.
If I had read the GTD book and read on this forum of Making It All Work, then I might write to my Collector: Buy Making It All Work.
During Clarification, I may remember that I have a reference list "My Favorite Authors" and I need to add David Allen to the list. As long as I'm happy that I have extracted all the value from the Collector's Item ( ! ), then I may add to the reference list and buy the book online without a Next Action.
Without the Clarify step, I may have lingering doubts about completion.