I think the right approach is basically "A Connecticut Yankee in King Arthur's Court". In Mark Twain's fantasy, his main character knows the basic principles of some modern technology, but the medieval period lacks any of the necessary material refining or manufacturing capabilities, so he has to work within the limitations of the time.

For this question, we are allowed to carry 15 tons of material from the present, which you can do a lot with. What could you bring that would actually be usable in the time period, and how could you apply it to actually change the course of events?

1918 is a very interesting time period to work in. Industrialization has spread, and automobiles have been around for awhile. Petroleum fuels are available for more than just lamplighting. Trains are not new at this point, but there are some interesting new ideas about not burning coal to make them run. The powered airplane was invented in 1903, and there was rapid development in this field between 1914 and 1918 due to the conflict in Europe. As WWI is drawing to a close, there's a lot of leftover military hardware lying around, and probably some supply officers who wouldn't mind writing off a few tanks in exchange for a bribe. There are opportunities that never existed before and never will again.

Practical application of radio is very new, accessible to only a small handful of people in the world who actually understand how it works. Battlefield communication is still largely done by hand-carried messages, with your best speed probably on a horse. Motorcycles exist, including military models, but the range is limited and they're definitely not all-terrain vehicles. Telegraphs exist but are dependent on wiring infrastructure. Communications is still difficult, and instantaneous communication in the field is nearly impossible - a problem that can be solved today with a $20 walkie-talkie.