What should I include in my letterhead as a sole proprietor?

That's it really.

Thank you!

You can put anything you want on your letterhead template. There are no rules you have to follow. Customarily, it is an extension of your marketing brand so you will often see as much contact information as possible beyond the basics you described. That would include but not limited to, business name, mailing address, physical address, office phone number, toll-free number, FAX number, website address, general contact email address, logo, and marketing slogan or jingle. You may want to consider right down to the colours, sizes and fonts. It is just another opportunity to advertise so make the most of it.

Sometimes the letterhead template is the parent template for other corporate documents such as an invoice, statement or other customer facing documents. If you want to convey a consistent brand or image, you should put some thought into how you might extend the basic letterhead to other uses, so as not to limit yourself with those secondary documents. For example, there are rules around what must appear on an invoice, so you'll need to accommodate the space for that in your template.

If you are just wanting it to send some simple correspondence and you don't really care about branding then most of my comments can be ignored.

foodieInTown limited
Toronto, Ont.
X1X 1X1

or if you're dealing with international/etc

foodieInTown limited
Toronto, Ontario, Canada
X1X 1X1

daivey wrote: ↑ foodieInTown limited
Toronto, Ont.
X1X 1X1

or if you're dealing with international/etc

foodieInTown limited
Toronto, Ontario, Canada
X1X 1X1

OP is a sole proprietor not a limited corporation. so no 'limited' can be placed after the name.

eonibm wrote: ↑

daivey wrote: ↑ foodieInTown limited
Toronto, Ont.
X1X 1X1

or if you're dealing with international/etc

foodieInTown limited
Toronto, Ontario, Canada
X1X 1X1

OP is a sole proprietor not a limited corporation. so no 'limited' can be placed after the name.

yeah for sure, i was just using an example