A homemade door dam. For a commercial version, see here.
a list of possible things to do:

  1. replace water soaked wallboard with paperless wallboard
  2. stop wallboard 1 or 2 inches above floor to prevent water wicking
  3. when replacing wallboard raise wall outlets above flood line
  4. replace paper backed insulation in walls with closed cell foam
  5. remove baseboards as soon as possible to let water in walls to escape and to dry sill boards
  6. use tile flooring throughout
  7. seal tile to prevent sewer water in grout pores
  8. fill bathtub with clean water to prevent sewer water from entering tub
  9. install a sewer line backflow valve
  10. don’t flush toilet during flood
  11. car ramps to elevate vehicle’s engine end
  12. seal exterior weep holes with closed cell foam backer rod (remove after flood)
  13. elevated garage shelving – and nothing stored on garage floor
  14. put bathtub caulk strip along all exterior door seams then climb through open window
  15. concrete dike (disguised as flower planters) around home exterior
  16. one or more bilge pumps with battery backup with hose out a window
  17. use towels to mop up seepage and spin dry in washing machine before each reuse
  18. remove bottom drawers of cabinets and place on counter-tops
  19. remove everything from under bed and closets and place in waterproof plastic boxes on top of bed
  20. remove any bedding materials that will wick water
  21. fold long skirts on hangers and use binder clips to secure
  22. install a permanent sunken sump pump plumbed out a sidewall
  23. enforce property elevation restrictions
  24. water sensor connected to wifi or phone to alert homeowner
  25. give a neighbor a key with instructions if leaving home
  26. put sandbags in driveway to prevent garage door damage from truck “wakes”
  27. roll up all rugs and put them on kitchen cabinets
  28. remove wet area rugs, etc., and dry in sunlight as soon as possible
  29. pick all power outlets off of floor prior to flood and use painters tape to secure them so they don’t fall in during the flood
  30. keep a box of nitrile examining gloves to wear during cleanup
  31. run dehumidifiers and fans immediately after flood
  32. assign neighbors to put up barriers when streets are flooded to minimize through traffic
  33. organize teams of neighbors to help elderly prepare for and clean up after the flood
  34. install French drains to remove standing water in yard where mosquitoes can breed – install a pump if necessary
  35. after the rain empty containers where water has gathered to prevent mosquito breeding
  36. move your shopvac into the house before the rain
  37. put flashlights strategically around the house
  38. alternately run the heater and air conditioning  – heat helps air absorb water AC acts as dehumidifier
  39. keep flood insurance up to date
  40. sharpen chainsaw before hurricane season – Dremel has a sharpening attachment
  41. mix 2-cycle fuel and stabilizer before hurricane season – store above water level
  42. pair with neighbors to cut fallen trees – safer and faster to work in teams
  43. wear chainsaw safety gear – Kevlar chaps, hardhat, gloves, ear and eye protection
  44. while the wallboard is off and everything has been dried out, paint the studs and sill plate with Kilz or similar to prevent future mold – use silicone caulk to prevent water from getting under sill plates
  45. Plant native grasses and trees that absorb water