Cycling Water Bottle - Bikes Water Bottle, Leak-Proof Sports Bottle | Bpa-fre Squeeze Bottle, Easy-Grip Design, Fits Standard Bikes Cages, Dishwasher Safe, Ideal For Roads And Mountains Biking

Does your backpack have a bottle pocket on the side? Do you actually carry around a water bottle in it? If your backpack has one of those pockets but you don't use it, get a cheap plastic squeeze water bottle (example) that is not transparent. Fill it with a node and your choice of antenna, close it up, and shove it in the pocket.