For now though, please expand up to Marin!
[Edit in response to comment below: I do not believe it is right to try something in a store and then go buy it online. Even if you believe that is okay, it actually proves that the purely-online consumer experience is sub-standard, otherwise why bother go to a store at all?
While Amazon is great at issuing refunds for, say, non-functioning electronics, they don't issue full refunds if you buy a hat and there's nothing wrong with it but it doesn't quite fit/look right, and you have to pay for return shipping. Contrast this with the Zappos approach where returns are both free, and hassle-free].
Do you have specific pain points, or is it the innate difficulty in online shopping for clothes?
Because so many of us (including myself) now behave in this manner, I'm fairly convinced that most brick and mortar stores will have to assume an "annual dues" model a la Costco to survive. (and offer some form of competitive advantage over Amazon, of course -- ex: focusing on item discovery rather than cookie cutter merchandise, etc.)
I do think Amazon has improved on this a lot. In the past I would find multiple listings, for the same product, from different merchants, under different names.
As an example, if I am looking for a specific Diesel jean I have waist, length, wash, and cut. The wash might be either described correctly, "0073N", or incorrectly "Dark blue." Looking at it now, this is much improved over where it was just a year ago.
On the other side of things, Amazon has a problem with fake products getting in their inventory by third party sellers being labelled as genuine -- another issue that has been getting better (The iPhone Charger listed as by Apple but priced like an iPhone app, was there for years.)
I pray that Newegg's diversification from computer hardware won't have the same adverse effect, but it's probably a law of retail that it will.
I compare my experience with Newegg, and although I've bought some stuff from Newegg, I will generally go with Amazon, even if it's a few dollars more expensive, because I trust Amazon so much more, and the entire experience is so much better. I'm basically their model customer, and they have me hook, line, and sinker, especially with Amazon Prime.
I cringe every time I have to order something outside of Amazon, dreading a MasterCard secure card, frozen order, mis-packaged products, and any number of other issues that affect my physical goods purchases outside of their system.
It seems that I only have good results when I search for a specific $productname, and even then I get results for products with user comments reading something like "its not $productname but..." or "get a $productname instead". More frustrating is that these seem to be ahead of what I'm actually searching fairly often.
Don't even get me started the self-published ebook spam -- is Amazon just ignoring it?
That's one of probably a dozen reasons why what works (or doesn't) for Amazon might be different for Instacart.
Also beer. Carrying cases of beer home sucks. ;)
If it bombs, it won't be because they can't keep the lettuce fresh from the field to your door, it'll be because you just can't do Ultimate Delivery for $99/yr.
Alternatively, if you're going to be doing this, you can purchase and register an IR beacon that is more permanent than a piece of paper.
And where exactly would you place the indicator? In your front yard? Normally, delivieries are made to your porch, but the drone would have difficulty finding an optical indicator on the porch from above.
And what about groceries that need to be refrigerated? Those will need to be dealt with specially.
In the foreseeable future, I think you'd have better luck delivering groceries by catapult than by UAV.