Someone suggested DIY kettebells using buckets full of rocks.
Well I have a partial alternative: I just upgraded my watering can with a bigger model which is quite a useful workout tool. You can't really do anything too vigorous with it or the water comes out (probably better than dropping rocks on yourself though) but you can not only adjust the weight depending how much water you put in it, you can play games like holding it at arm's length in different poses while filling it from the tap and trying to hold it still as the weight increases.
Then you get to hold it up high to water hanging baskets above head levels, hold it in different positions while watering pots and tubs - the different handles provide differing amounts of leverage - walk about swinging it around, etc.
And even if it doesn't help your fitness much you still end up with flowers and vegetables.