Gaffer's tape is the ideal duct tape alternative (VIDEO).
Gaffer Tape vs. Duct Tape: What's the Difference? - Tape Jungle
Nashua Tape 1.89 in. x 55 yd. 394 General Purpose Duct Tape in Silver 1529728 - The Home Depot
GaffGun GT Duct 500 Pro Grade Duct Tape (3" x 50 yd, Black)
Amazon.com: YYXLIFE Premium Grade Gaffers Tape, Heavy Duty Non-Reflective Matte No Residue Gaff Main Stage Tape,Electrical Tape,Duct Tape for Photographers,Waterproof Gaffer Tape,2 Inch X 10 Yards, White : Industrial & Scientific