As an example, I asked my employer if I could borrow my steel toed boots meant for site visits to use during some work outside to help a friend for a weekend. I told them if I damaged them I would gladly pay to replace them. My boss told me that they would lose much more value from me missing work injured than those boots would cost to replace, so not to worry about it and then gave me a fatherly lecture about being safe using a chainsaw before digging out safety glasses to send with me.
It's hard to make a bright line for abuse, but for a general rule I won't take anything or take advantage of anything I wouldn't pay for myself without asking ahead of time.
Personally I stick to water because HFCS is bad for you.
My beverage of choice is Ito-En bottled green tea. I'd prefer if it came in glass vs. plastic bottles, though, and it is $1/bottle even at Costco, so at home or office I tend to just make my own using either matcha teabags (also from costco) or looseleaf green tea.
Going back to the topic of expense to the company - healthier foods are also generally more expensive than junk food. But if you think it's worthwhile to keep employees at optimal performance, it's a small price to pay...
Look at why it is provided. It's not a prize or a bonus. It is to keep you happy and productive while you work. The company feels that is worth the cost. Where in there does someone drinking soda on the way home figure? It doesn't.
If I were the person providing the free soda I would be upset at being taken advantage of.
Finishing your soda on the way home, sure. Grabbing an unopened one and walking out the door... that seems to me to be a good place to draw a line.