Cans of food such as soup, especially the bigger cans are probably around 3 pounds. 1.5 litres of water is just over 3 pounds so a bottle that size would work. If you have a food scale just weigh some different cans and bottles and pick whichever is closest.
Three pounds of weight isn't going to build any strength! Try doing a Google search for bodyweight exercises. You can do squats, lunges, push-ups, crunches, etc. (modified for your fitness level if necessary) without buying any equipment and get in pretty darn good shape!
Thank for your suggestions Changergirl & stella1609.
I have been doing 30 day shred by jillian michaels and it has been working real well on the flabby areas. the requirement of weights just got me thinking about substituting them.
but would be really glad if it's possible to go ahead without weights. as it is quite challenging without the weights themselves.
is it also fine not to use any while doing so?