IF the seeds are mature enough that you are concerned with carrying them out, then you should be carrying a bag to place them in, as soon as you cut them off. Otherwise, if you just carry out the plant, you may be spreading seed the whole way along when you carry them out.

One idea to consider - if you need to:  carry a bag along. Cut off only the seed heads of those that seem mature enough to spread seed. The rest of the plant - and the rest of the plants - you can cut them off and let them lay.  (or pull and let lay).   The seedhead is the only part you need to be concerned about. (But you already know that.  :)  )