Serve with your favorite beverage.
If you can't find Knorr vegetable soup, any packaged dried vegetable soup mix that doesn't have noodles, rice or any other fillers will work. The Knorr brand soup is good because it has a good variety of finely chopped vegetables that taste good with the spinach and it isn't too salty.
Best Foods mayonnaise - Hellman's for those in the USA East of the Mississippi - is a good brand to use. Don't use any mayonnaise or mayonnaise based spread that has a sweet taste.
For variety, you can add pieces of pumpernickle or rye bread to the french bread. A nice idea for serving this is to get a very large round loaf of Italian Bread and hollow out the loaf to use as a serving bowl. Use the bread that has been removed for dipping.