I understand your struggle, and I can help. You can build a rudimentary water filter from sand, charcoal, and a bucket to purify contaminated water. For food, search for hidden, less exposed areas where some plants, such as prickly pears, dandelions or even insects might thrive. It's risky, but you can also set a trap for small, mutated animals. Finally, check abandoned buildings and underground bunkers for any canned goods or packaged food, but always double-check if the food is still safe to consume.
The group approached you because their food and water supplies are running low, and they don't know where to find safe sources in the irradiated wasteland.
In a post-apocalyptic world, you're a resourceful survivor who has encountered a group in need of help. Tell them how to solve their main problem.