Slip & fall case

The value of your case is fact intensive and depends not only on the liability but also the damages. For example, your case has no value unless the "well-known store" is negligent. In other words, was the "spill" a foreseeable danger that could have been prevented? There have been recent Massachusetts cases that address this type of liability.
If the store was negligent then you are entitled to damages including but not limited to out-of-pocket expenses, reasonable and necessary accident-related medical expenses present and future, accident-related lost wages and/or lost income present and future, and pain and suffering damages.
Even if no liability exists, you may be entitled to some benefits for accident-related medical bills from the store's med pay insurance policy.

The value of your case really depends on the specific facts of your accident and your injuries. There is no "formula" for figuring out the value of these types of cases such as 2-3 times the medicals. Much depends on the liability of the store, whether you were partially at fault and the nature and extent of your injuries. The kinds of things you can recover for are medical bills whether or not they are covered by insurnace, lost wages/loss of earning capacity, as well as pain and suffering past, present and future. To hold the store liable you need to show that the store either knew or should have known about the spiil and had a reasonable amount to time to discover the spill and clean it up, or provide warning. You can also prove notice in some circumstances if by their mode of operation it was forseeable that these types of incident swere likley to occur and they failed to take adequate precautions to either prevent them and/or discover them.