Garage/Yard sales are my biggest summer bonding events with my father. Usually, we look out for vintage speakers, receivers, and turntables, as well as vinyl. It's sort of a hobby of ours to restore and fix broken stereo equipment, and it's honestly a great way to make a quick profit if you're willing to put a bit of work into it.
That's awesome that you share that with your father! Sounds like a great time.
Non-power tools, sofas (!) or other furniture you can fix up (make sure there are no smokers in the home), baby toys.
Sure the wife and I may look for household items as well. What I was thinking was pipes, shaving, luggage, etc. Anything else more of interest?
Another great find is cast iron cookware. It's the best way to cook food, and also can turn out a bit of profit. Hunting craigslist for wood stoves is a good move to make in the summer months, where you can get them cheap and hold on to them until winter, where people will shell out a lot more for them.
Good idea! I'll second if you can find them. Cast iron is still available and there is still one brand I'm aware of made in USA (Lodge), but it's becoming uncommon, which is a shame because it's a screaming value for longevity. As long as you don't drop them on something hard (cast iron is somewhat brittle for a metal), or soak them in water, they'll last around a century or more and used to be hot items to pass down generation to generation.
The typical thickness helps even out hot spots, the "seasoning" and dimpled texture create a natural partially "nonstick" coating, and whatever iron leaches into your food is a useable source of nutritional iron for your body. Avoid enameling as it can't take as much heat, will eventually crack one way or another, isn't as non-stick as a seasoned pan with a sandy texture, and lacks some of the other cooking properties of unglazed cast iron.
Things that have lids are a real find. You can use a cast-iron pot with a lid as a slow-cooker in a low oven, or crank up the heat and use it like a baker uses a steam oven to make bread with a thin crackly-crisp crust that "sings" as it cools. With or without lids, cast iron is fun to bake bread in--but watch the temperature and time as it will bake faster than in other types of bakeware. You can get a really nice oven spring if you're careful not to burn it! Try Jim Leahy's no-knead bread; you can make a fresh artisanal loaf stupidly easy, that would sell for around $5 in a fancy bakery.
Cast iron might very well be a "man's choice of cookware", because I see it in hardware stores and sporting goods stores, not kitchen stores (except the enamaled kind that I don't recommend). It's kinda heavy for women and children; my wife doesn't like it.
Unfortunately, I'm not able to do the weekend gigs because of my job. However, I'm always on the lookout for Vintage Railroad lanterns, National cash registers and hand powered antique tools. Things along those lines are what I like to refurbish. Some I keep, some I sell.
Really getting into the shaving thing lately so looking for hones, whetstones, razors of all types, shaving cups and other accessories. For some reason, I like to sharpen things from large knives all the way down to drill bits.
Cast iron anything, especially ones with lids as Rob suggested. Sometimes only the lids can be found and I'll buy them for a pittance.
Old tools for personal use and to teach my kid (and the neighbors kids) how to use their muscles and brain to work with wood.
And any old weird stuff that the people selling have no clue about what it was used for. Sometimes I have no clue either, it just looks interesting. Usually they just want to off-load it.
Haggling is fun and exercises your brain, although I don't do as much of it as I'd like. I know some expert hagglers.