Design a Duration that is either "Now and at the start of your next turn" or "Either now or at the start of your next turn"; Ideally, the card should not do other things - for example, Caravan wouldn't qualify as this, since it doesn't give +1 Action next turn; or Royal Galley (although it would if it also gave +1 Card on your next turn). The focus should be on the benefit from the "now and next turn" action, rather than something ancilliary.
So for official cards, Lighthouse Wharf would count for the former, or Barge would count for the latter. A non-exhaustive and lazy list.
As for additional rules, I'm not going to disqualify entries, mechanics, traveller lines, split piles, yadda yadda, but one of the core tenets you should be aiming for is to keep it simple. You will engender a great deal of goodwill from me, who will be judging, by keeping it simple.
Please let me know if you have any questions. Contest will close 5/12, around noon EDT, with judgment to follow.
also i was going to title this contest "( Now and Later ) xor ( Now xor Later )" but logic-wise that reduces to "Now or Later". oh well, i can be clever some other time.
Shout out to LibraryAdventurer for this suggestion in the suggestion thread.