The best replacement for panniers is backpack.

The best alternatives to panniers are rated as following:
★★★★★  backpack
★★★★★  trailer
★★★★  top box
★★★★  trunk bag
★★★★  basket
★★★  saddlebag
★★  backpack cycling
★★  rucksack
★  messenger bag
★  trailers
★  bob trailer
★  touratech
  rear rack
  saddlebags

Your alternative for panniers is not listed? Suggest!
Speaking about panniers, one probably shouldn't forget about child seat.

Other search terms related to panniers and their ratings are:
★★★★★ child seat
You have in mind a companion for panniers and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of panniers in all years. Click on graph for more.
panniers
backpack
trailer