This is actually my first post after months of lurking. Your post inspired me to share my findings. Sorry in advance for the wall of text (I like to be thorough). lol
Hands down my wife and I love the Skechers Gowalk series of shoes, specifically the GoWalk3 series. We both have wider than normal feet and our feet tend to swell when we walk all day in the parks. We each haved owned 4 or 5 pairs and always bring a new pair (worn for 1 week prior to visit to break them in) when we visit the parks. During our first visit in 2014, we wore normal shoes and regretted it so bad for our second trip we decided to invest in these shoes and I'm so glad we did. I also own two pairs of the GoWalk4 series but these are sized differently and although are almost as comfortable just feel different. One thing to note about these shoes is they don't last very long (about 3 to 4 months of normal daily walking) and are a little expensive as they usually run $50 to $60 a pair. You can get them on sale at a bunch of places though like Zappos, 6PM, Shoes.com, etc, etc for around $40 if you're lucky.
I swear by the Balega Hidden2 Dry socks. I have a really bad reaction to cheap all-polyester ankle socks and usually wear 90%+ cotton socks, but these are absolutely excellent. These are expensive, like $10 to $12 a pair expensive but OMG they are so worth it in the long run. I've only ever been able to purchase these in quantities more than 5 from
Amazon for a decent price.
To prevent blisters, wife and I both use paper tape which can be bought at Dollar Tree across the Achilles tendon and on the outside of our big toes. We typically go through about 1 roll every 3 days for two people with large, wide feet (I wear a size 12 to 13 men's, she wears a size 10 women's).
We also use Dr. Scholls Sweatmax spray between toes and on the bottom of our feet to stay dry. We
do not use lotion while we're touring the parks because it reacts with the non-cotton material in most socks and causes excess slippage. The Dr. Scholls spray acts as a friction powder in a way which I love. We go through about 1 can every 5 to 6 days when at the parks. If you or your spouse's employer(s) offer(s) FSA (Flex Spending Accounts) or HSA (Health Spending Accounts), many times you can buy this spray at Wal-Mart using that account or get reimbursed for several cans at a time. Also, I recommend that you only purchase this from Wal-Mart or Target. They tend to have the best pricing on this item from what I can tell.
With regard to sling bags, I have to recommend the Patagonia Atom sling. I LOVE this bag with one exception. It's small, lightweight can hold two 1L water bottles, and isn't too pricey. If you look hard enough you can find it on sale between $35 and $45 at different places if you aren't picky about color.
The one exception I mentioned above is that I started using a hydration pack and now am totally spoiled. No need to refill if I'm not sharing...which I don't lol, wife has her own now too) I can't live without that bag when I got to parks now, especially during Summer! I have Ogio's Dakar 3L which has now been discontinued for some reason, they have a new one though call the Atlas. In addition to the hydration bladder, it also has plenty of room for my GoPro gear, supplies, snacks, poncho/jacket, etc. It is NOT a sling though, which I actually don't mind since it sits up high on my back like a sling, but I feel more "strapped in" with it on than a typical sling. It IS however about 60% of the size of a typical backpack, making it much smaller, lighter, and means you can't cram as much into it.
Shoes (Women):
https://www.amazon.com/Skechers-Per...1507683780&sr=8-1&keywords=skechers+go+walk+3
Shoes (Men):
https://www.amazon.com/Skechers-Per...1507683780&sr=8-2&keywords=skechers+go+walk+3
Socks:
https://www.amazon.com/gp/product/B00CBAI798/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Paper Tape:
https://www.dollartree.com/Royal-Paper-Tape-for-Sensitive-Skin/p302003/index.pro
Foot Spray:
https://www.amazon.com/Dr-Scholls-S...684144&sr=8-4&keywords=dr.+scholls+foot+spray
Sling:
https://www.amazon.com/Patagonia-48...qid=1507684316&sr=1-1&keywords=patagonia+atom
Ogio Hydration Pack Alternative:
http://www.ogio.com/backpacks/hydration-packs/atlas-3l-hydration-pack/spr4704859.html