-Retargeting/Remarketing - Some of your best ROI campaigns will come from these
-Discount Ladders - for customers to nudge over the edge great to use in combination with the retargeting campaigns.
-Abandoned cart email follow ups - No mention of these here. Again, these backend flows will really help profitability.
Ideally you'll break even on those leading awareness/acquisition campaigns using the things others here have said and the retargeting campaigns will be nothing but gravy.