What they said. The Chalean basic set comes with two resistance bands, and the Deluxe set with three; those are probably your best non-dumbbell option. If you didn't get those, individual resistance bands are available anywhere with a fitness department, for about $10 each; I prefer the rubber-tubing kind to the elastic kind. You'll probably want two: a 'lighter' band for small muscle groups like the biceps and triceps, and a 'heavier' band for big muscle groups like chest, back, and quadriceps.
If that isn't an option, I've known people who started working out by lifting soup cans and water bottles. Whatever you use, it should be small enough to hold in one hand, heavy enough to cause fatigue at 10-12 reps (6-8 in Phase II), and something that you can safely lift over your head (no bleach bottles or marble statues.)
"Standing on the defensive indicates insufficient strength; attacking, a superabundance of strength." -- Sun Tzu
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