The trail does go over several steep rocky passes, and lakes are abundant. It's hard to give a detailed description of the trail over 182+ miles, but you'll have steep ups, steep downs, long gradual ups, long graduals downs, and flat terrain here and there. There will be several river crossings, up to and including waist deep water. You're pretty much guaranteed a beautiful lake every few miles, with some of the most beautiful campsites you'll ever see.
Some of my favorite lakes that I camped at were, and would HIGHLY recommend fitting into your camping schedule: Virginia Lake, Marie Lake, Squaw Lake, and Thousand Islands Lake. There are more, but those 4 stand out in my mind because of how amazing they looked. The stars are AMAZING and the lakes are some of the least light polluted areas to see them, so if you plan your trip right, and you're not out there during a full moon, you'll be able to see the Milky Way and much more.
Places to resupply for long outings:
Has a small grocery store, pharmacy, and many restaurants including an all you can eat Chinese buffet. Lone Pine also has a great gear store, and cheap camping up Whitney Lortal Road, within walking distance of town. A hostel is also available.
Independence (via the Kearsarge Pass Trail):
Has a few restaurants, motels, and a gas station where you can resupply on limited items. There's also a post office for boxes.
Bishop (via Bishop Pass Trail):
Has big grocery stores like Smiths, and the local hostel is a must! Movie theatre, multiple gear stores, just about anything you need exists in Bishop. You'll want to get a hitch into town from South Lake, which a fairly easy alternative to the 25+ miles on foot.
Mammoth (via Reds Meadows bus):
Huge town, has everything you'll need. Bus fare was $8.00 for the round trip from Red's into town and back. Camping at Red's is about .5mi from a grocery store. Red's has pay showers, laundry, a restaurant and store. The Hiker box during peak times is awesome.
Muir Trail Ranch:
Hiker boxes are abundant during peak JMT times, it will probably be the best you'll see the entire trip as well. charging strip, but you might have to wait in line... Ranch staff charge $75.00 for package pick up/holding if you ship anything there. Staff is strict on opening and closing times. There is free camping near the river, with hot springs across from camping area. The hot springs are dirty but warm. The river has lots of trout. No food and small store with overpriced items and pay by the minute internet.
Vermillion Valley Resort:
The resort offers free beer for through hikers of JMT or PCT upon arrival. Beware, you can rack up a bill fast here. There is a great restaurant and store. Visitors can use pay showers, or take advantage of the resort's work-for-stay/meals program. There is free camping. Don't be surprised when items from the hiker box appear on store shelves. Overall there is camping, cheap beer, and expensive food, but you'll have a good time. They also offer a ferry, call them for rates and info. I took the Bear Creek Trail into V.V.R., there is also a bear ridge trail that gets you there. Bear creek is easier, and the 2nd split off to the left. Accepts packages for a fee.
Expensive! The post office is slow in receiving or process your items. A local store has a good supply, but items tend to be expensive. There is an expensive resturaunt next door. Campsites are available nearby, which are cheap and out of the way. The store has a charging station, ATM, bathrooms. Showers are available at the Toulemne Meadows Lodge at the last bus station. The campground gets crowded, so expect to see others! Lambert Dome is .5 mi away and is a must do rock scramble for sunset, WORTH going to!!! Limited cell service available here, might be able to make calls or possibly get a text out depending on provider and location.
Black bears are very present! Make sure to have your bear canister! Rangers will check for permits and bear canisters and write tickets if you don't have either. Please respect the rangers, as your own safety is the goal.