Jdale's suggestions are all good ones. I've run a low-magic campaign in a nomadic setting, off and on for about 30 years, and adventures are definitely a challenge if you don't want to just run constant 'tribal conflict' scenarios. Here are some of the things that have proven popular with players:
Horse thieves: someone is stealing horses or other livestock, and the party is asked to investigate, or has some of their own stolen. It turns out that it's not just a local problem and it's an organized band of thieves. Scale as fits the power of the party.
Romeo and Juliet: Arranged marriages and marriages for political alliance were common in nomadic cultures. You can do a straight R&J scenario of lovers whose tribes/clans are rivals, or you can flip it and have two clans trying to arrange a marriage but the bride or groom refuses and flees. Either you have interclan combat and drag the party in one way or another, or you have a pursuit to find a reluctant bride/groom. Lots of opportunities for noncombat roleplay.
Natural extremes: Drought, flood, prairie fire, snowstorm - take your pick. They all have a big impact on nomadic life. I just played out a "natural" disaster in my campaign, with a wave destroying the fishing district in the city, and the players said it was one of the best sessions they've ever had, trying to figure out what they could do when there's no attackable enemy, no one you can talk to or influence. Can you safely get the livestock to new food? Do natural predators lose their food supply and get bold enough to come attack herds?
I also have one animal species that goes through population explosions every several years, in various regions. At that time, they become aggressive and start destroying the livestock herds. Adventures could range from protecting the herds, to actively going into the lair of the creatures to clear them out.
Remember, Chinggis Khaan started creating his empire by fighting, conquering, and allying with neighboring tribes. They were always at war, and there's no limit to the plot lines you can draw out of that kind of environment if you want a lot of battle and diplomacy. The 2007 movie Mongol can give you some inspiration (and an awesome soundtrack to drop in the background of your sessions.)