Experts say YES to molasses! Terrific bagel tutorial on Ruhlman's site-
http://ruhlman.com/2011/01/bagel-recipe.html

I would use brown sugar 1tb as a substitute. King arthurs has what you need for next time.

I have never heard of adding malt to a bagel. But I have always added about 2 tbsps of molasses to the boiling water - it gives the crust a deep color and hint of that molasses taste.

Malt powder comes in two forms: diastatic and non-diastatic. Diastatic malt contains enzymes that break down starch into sugar; this is the form bakers add to bread dough to help the dough rise and create a good crust. It is food for the yeast.

Malt syrup is made by malting barley grains to produce maltose, a type of sugar. Its unique flavor and rich, dark color is used by bakers and beer brewers. It is a sweetener. The people at King Arthur Flour maintain that their syrup improves the shelf life of the baked product.

Malted milk is a powdered food product made from a mixture of malted barley, wheat flour, and whole milk, which is evaporated until it forms a powder. This is what's in Ovaltine and in Whoppers.

To answer your questions: (1) The malt is not crucial. Your recipe probably calls for only one or two teaspoons of malt powder (any more than that and your bagels will be overproofed, hard to handle and will taste like they've been dunked in beer). The substutute for 2 teaspoons of malt powder is 1 tablespoon of honey, malt syrup, brown sugar or molasses. (2) The shelf life of malt syrup is about three months after opening the container. (3) Sorry--malted milk powder only for the Whoppers, but you could make popcorn balls or caramel corn or spice cake. Some people put it in their oatmeal. Or you could make beer! Yay!

My bagel recipe is from a 25-year-old copy of the "Chicago Tribune." It does not call for malt powder. The bagels are dense and chewy without being rubbery. They taste very plain, almost bland, so I coat them with a mix of kosher salt, cracked pepper, a hint of garlic powder, poppy seeds, sesame seeds and sunflower seeds. There is no recipe--I just dump stuff into a small bowl until I think it looks good, then I brush the boiled bagels with egg white and dip them in the seed mix before baking. The mix is so yummy that it would make a rubber shoe taste good.

I think molasses will be too strong as a sub for barley malt. I don't know about syrup subbing powder - it makes sense if you were to decrease the amount of water in the dough - but you will probably find many uses for barley malt syrup if you do purchase it. It is much more mellow than molasses or honey but can sub for either and has a very long shelf life. Good luck with your bagels!