There's no way to determine if an item is safe to sell without looking it up online. Even items which have descriptions which make it sound like they could be sold might still have a use. In fact, the Silver Egg is a perfect example of this. The item description says it's "of no use to a hunter", but it's used to craft Fate Jewel 1.
Kiranico is a fantastic resource for any hunter, and contains searchable information on all of the items in the game. It's your best bet to determine if a specific item is safe to sell or not. The sources tab shows you all the places you can get that item from, and the usage tab shows you the various uses of that item. If the item shows up under the uses tab, then it isn't safe to sell. The uses tab doesn't list all possible uses though, strangely enough. So you'll want to check the Veggie Elder, Hunting Fleet, and Villager Request pages as well. Finally, you'll want to double check this page on farming, to see if an item is also used for upgrading the farm or acts as a fertilizer. If the item doesn't show up on any of those pages, then it's safe to sell.
Here are some links to read more about the Veggie Elder, Hunting Fleet, and Villager Requests, just in case you're not familiar with what they are.
I've compiled a short list of some of the items you can safely sell, but this is not a complete list:
With that said, if your main concern is making money, then these safe to sell items aren't how you'll make most of your cash. The best way to make money is by selling monster carves from large wyverns (Great Jaggi, Rathian, Barroth, et ceter). These items are used for crafting weapons and materials, but unless you plan on crafting every weapon and item in the game then you're not going to need every carve from every monster. Kiranico is a good resource for determining which armors/weapon you want, and by extensions which monster carves you don't need.
Farming is another good way to make money, although by the time you hit G-Rank it'll be completely outclassed by monster carves. The Monster Hunter wiki contains a good article on farming which I'd suggest reading. The important thing to take away from it is that farm yield is increased by using fertilizers. Using fertilizers to increase yield is very important if you want to make a good profit from farming. Nulberries are my preferred item for farming. Just check your farm every few hunts, replant a few Nulberries, and then sell the rest.