Unless you are extremely weak, a can is not going to give you much of a workout unless your normal workout is doing resisted cadio with pink dumbells.Think about it, when you brought that can home from the store, you likely carried it into the house with many other cans, boxes, etc. and don't even think twice about it, so how can lifting just one can out of that bundle be considered a workout.
If you want resistance without weights being handy, do bodyweight exercises. Hit those pushups, lunges, bodyweight squats etc. If you want to increase the difficulty, rather than adding neglible resistance from a can, add some isometric holds or simply reduce the tempo to up the time under tension.
Here's one premade bodyweight workout from Alwyn Cosgrove to give you some ideas: "Your Body is a Barbell"
http://www.alwyncosgrove.com/bodyisabarbell.htmlSome of these may be too advanced for you if you are just getting started, but you can always modify. Skip the single leg for example or do the pushups with your hands on the third stair of your steps or on a coffee table, etc.
If you really want to lift, go out to the back yard and find what Dan John calls a BFR2000 (Huge rock). Do presses, squats, farmers walks etc. Get a couple of very strong garbage bags and fill them up with some sand and do sandbag exercises. Unless you have some duct tape handy and something like a backpack or dufflebag to put the garbage bags in to make more durable, I'd use these outside only.
You should be able to find something around the house bigger than a can, unless we are talking about some sort of drum. Even the largest of vegetable or soup cans etc are not going to give you a workout (regardless of what Denise Austin may tell you). Find something heavy or use your own bodyweight.
Impromptu weights
