Welcome, Stan!
Are you hiking southbound? What are your start and end points for your trip?
I’m going to assume that you’re looking for an online map for research, as their is no “online” when you’re on the JMT.
I will say that there are only a few places where you can easily buy food within an easy detour off the JMT:
- Tuolumne Meadows
- Reds Meadow (near Devil’s Postpile)
- Vermillion Vally Ranch (VVR)
The stores at these locations are small and may not stock exactly what you’re looking for. What most people do is ship a resupply package to these locations and then supplement with just a few items from the stores.