How long are you staying? How many people will you have? Ages? I'm wondering about children in the car seat age range, mainly. If there's kids needing car seats, I'd use the Disneyland Resort Express (DLRE), basically just to avoid having to install car seats in an unfamiliar vehicle. (I don't trust rented seats--has it been in an accident? Vomited on? Peed on? Cleaned appropriately [yep, there's a correct method to cleaning car seats]? Will they bring/have the appropriate seat for my child's height/weight/size/age? Lansky's just replaced their seats about a year ago, after having a fleet of expired seats, and drivers with no clue how to actually install them.) Yes, DLRE can be a pain--having to walk a few hotels from your stop when you get dropped off, and then another (possibly different) spot to be picked up. They aren't very punctual either. But, for the price (are kids still free?), it's a pretty fair deal. And an even better deal if it means not having to install car seats more than necessary!
As far as the grocery stop goes, I've always meant/planned to do Von's, but in all reality, it's rarely ever been needed, even when DD8 and I stayed for 8 days. We found we just never really ate in the room/hotel much, other than maybe at breakfast and a midnight snack for me after she was in bed. Tropicana (next door to Camelot) has a small market with basic necessities, some frozen food items, milk, etc. If there's something we need "often," I usually would just pop into whatever market was nearby. A little more expensive, perhaps, but the money I'm saving my not taking a hired car would make up the difference. Of course, if you have a family of 8 or such, where 8 breakfasts at the minimart would be cost-prohibitive, there's always Vons as well--free delivery on orders over $50--and delivered right to the hotel's front door. Or
Amazon Fresh delivers to the resort area as well, if you are a Prime member. I don't remember how long Lansky's will stay for the grocery stop--20 minutes?--for me to shop, even for just essentials, for a family of 8 (that's what we currently have at our house!) would take me longer than the allotted time. (And holy cow, keeping several kids in the car with DH/DD23/Son-in-law while 1 or 2 adults went in to conquer it? There would be mutiny!) But, I also am completely terrible in new grocery stores, and get annoyed/frustrated when I can't find what I'm used to, in the place I'm used to it being.
It's a tough decision, obviously!