I am traveling to Australia after 2 weeks. There are multiple domestic flights I am taking to go from one city to another in Australia. I found that in all of my domestic flights, I have to pay extra for check in luggage. So, what I was thinking to do is take 2 bags with me of following types:-

1. Laptop Bag
2. Trolley bag of 55 cm(example: here)

Is it okay to carry 2 cabin bags in domestic flights? I live in United states and I know here it is allowed in almost all the flights. But I am not sure about Australia. I know it might depend on flights also. So, I am listed down the flights that I am using in Australia over here as follows:-

1. Jetstar
2. TigerAir

Also, do someone check the weights of the bag? I know the max. allowance is written as 7kg for cabin luggage but I never saw anyone checking about. They normally just check the dimensions at maximum. And say, if it get checked, what is the kind of fine that most airlines imposes and then does it go as the check-in luggage or cabin luggage.