Okay, I have seen several times where you can buy a refillable mug of some sort for around $12 that you can refill at your resort restaurant the entire time you are a guest. My question is - how big is it? Is it made out of fairly sturdy material where we could carry it around with us? I am thinking we will eat an easy breakfast at the resort, stick the cup in my backpack/purse and then just carry it around cause I assume it would be a fair distance back to our room to leave it. Or is it too big/fragile/whatever that this would be impractical?