Uses for sodium nitrate (from the search engine)
Convert to sodium nitrite by adding it to molten lead, then filtering off the lead oxide (UTFSE for a more detailed writeup)
Also in "PART 2 of 6: LARGE SCALE OLD SCHOOL METHAMPHETAMINE PRODUCTION"
And, what I remember it from - explosives, smoke bombs (smoke bomb recipe says Potassium Nitrate, however sodium nitrate can be substituted)