The best replacement for backpack is messenger bag.

The best alternatives to backpack are rated as following:
★★★★★  messenger bag
★★★  suitcase
★★  briefcase
★★  shoulder bag
★★  backpack
★  basecamp
★  rucksack
★  bag pack
★  duffel bag
★  daypack
★  panniers
★  handheld leaf blower
★  laptop bag
★  luggage
★  bookbag
★  handheld blower
★  diaper bag
★  messenger
★  purse
★  wheeled luggage
  tote
  messenger bag college
  rolling luggage
  internal backpack
  external frame backpack
  laptop backpack
  evernote
  walk behind leaf blowers
  back pack
  tote college
  handheld
  brief case
  internal
  internal frame backpack
  suitcase europe
  sling backpack
  satchel
  book bag

Your alternative for backpack is not listed? Suggest!
Speaking about backpack, one probably shouldn't forget about harness.

Other search terms related to backpack and their ratings are:
★★★★★ harness
★ wheels luggage
You have in mind a companion for backpack and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of backpack in all years. Click on graph for more.
backpack
messenger bag
suitcase