AT&T, T-Mobile and Sprint also offer a similar deal that Verizon is offering. AT&T and Sprint are offering credits like Verizon for activation and 3 months of service. T-Mobile's offer is just free activation and 3 months of free servcie.
I haven't seen any deals with Apple Watch series 3. But you can get some discounts through credit card. For example, if you have a Chase credit card and use chase pay, you can get 10% off at Walmart and Bestbuy. Depending on your local sales tax, it might save you a little bit.