I don't think that many of these requests are rude and inconsiderate. And I'm certainly not convinced that mayonnaise is stupid, random or obscure.
It sounds like you don't really like these friends and family and like you hate hosting, so you should stop inviting them round
The person who asked for rock salt was helping you prepare a salad for a party which I can only presumably YOU were hosting.
If a friend roped me be into party prep I wouldn't think it was outrageous to ask what ingredients were available.
Asking for Mayo definitely isn't rude. All you have to do is say no. It's a fairly standard condiment.
Asking for salad IS slightly odd IMO. As that's materially changing the meal and seems to be somehow saying OPs sandwich isn't good enough.
BUT I also think feeding an adult a plain cheese sandwich with no condiments or salad on offer is also odd. I would find it hard to eat something that dry, and if I'd been invited over for lunch I'd be slightly surprised.
If someone offers you a coffee/ tea/ cereal - saying do you have skimmed / semi / full fat milk is fine. As long as you don't kick off when they don't.
Likewise asking about brown sugar isn't strange. We don't keep white sugar in the house (I don't think) but if someone asked I would double check and say sorry no if I didn't. I certainly wouldn't find them rude for asking.
Also - I do believe that hosting is about giving people a good time. I have a friend who drinks sparkling water. I don't touch the stuff but always get some in when she's coming.
Another friend is vegan so I buy almond milk for their coffee. A third friend is a real hommous fan so I usually buy that and crisps for them even tho I don't like either. Also I don't drink tea at all but I keep teabags in for visitors and tradesmen.
I like Diet Coke and my friends usually have a few tins of that for me when I come round. Etc etc.
It's not rude to ask. It's not rude to say no if you don't have something. It is rude to not get things in that invited guests like...