Lori, your profile doesn't say where your are but here in Texas, I've done a few searches and have gear designed for our climate.
When the space shuttle Columbia went down, I did several days of searching in East Texas...in sleet, rain/mud, and learned a lot from that search. The only over night gear carried stayed in the van, where I slept. Searchers came in at sundown every day, and re-grouped in the morning. So, I didn't carry anything in my pack for over night other than a Robinson poncho, space blanket, and other emergency stuff. I've yet to participate in a search where overnight camping was expected.
I learned that a rain suit worked well for most situations...until...we got into clearcut and deep forest. My rainsuit is now a punctured mess due to the wild rose and brier. Barbwire fence will destroy your rain gear.
I now wear Walls...yes cotton...coveralls, both insulated and not, that I've waterproofed with a good DWR. NOTHING gets through those. I've been soaking wet and they were still warm. In summer, military utilities work well but you still want to be protected from stickers and barbwire. Good tall, waterproof boots are a must....walking up a cold creek seems to always happen in searches.
I'll haul an umbrella and rainsuit sometimes, and park under the poncho in really heavy rain. My pack is a Go-Lite "Day" and seems to hold up great. I bring at least one ski pole as a trekking pole. I could spend the night if I had to.
Just remember, in a search, you are working tasks that are more demanding and unexpected than a pleasure trip. Ultralight has it's place but most gear needs to be heavy duty and in some cases, expendable.