"It probably would be best to use the sentence/slogan with the TM symbol without federal registration. Maybe one day it might acquire secondary meaning. Who knows."
That sounds like a good plan.
Re: Secondary Meaning- Someone can correct me if I am wrong, but even if it is descriptive (and not suggestive), you still should be granted allwance on the Supplemental Register (provided that the slogan is not likely to cause confusing with another existing slogan). Though much weaker than the Principle Register, you'll have a placeholder for your mark, and after 5 years of continuous use, you can petition to be moved to the Principle Register.
For a service, I believe advertisments, brochures, business card/stationary showing the mark (here, the slogan) with the service, and business signs are acceptable.
For a product (?which may be more applicable for your situation for pasta), I believe a display for the product would be acceptable (in addition to packaging). I don't think advertising/business cards or stationary would be sufficient for the product.
Just curious... Are you affiliated with an advertising agency that is creating advertising for a pasta company? Or, are you affiliated with a Pasta company that wants to use a slogan in their advertising? I would say that clarification here is important. If you are an advertiser separate from the manufacturer (and contracted/hired to create advertising), than I don't believe that you could claim trademark protection in your slogans (as trademark protection is created by use of the mark in commerce in the classes where protection is sought- your ad agency is not in the business of selling pasta, so you are not using the mark in commerce). In that case, your rights to the slogan(s) you geerate would likely be defined by the contract between your ad agency and the company (and their rights to use the mark would be defined in that contract as well).
Now, if you work in the advertising department of a pasta company, then it would seem that your comany would have some sort of packaging to get to the next vendor in the chain (if not the end consumer), and could place the mark/slogan on the packaging, or ultimately, a product display that is placed by the product at the point of sale to the end-consumers (i.e., supermarket). Your use in that fashion could be sufficient for the pasta company to aquire trademark protection, provided the mark/slogan is used with the packaging or product display.