This was probably the collection My Friend Mr. Leakey, by J. B. S. Haldane (1937). In the first story, "A Meal with a Magician", the magician Mr. Leakey gives the protagonist a mango that he's enchanted to not make a mess:
'About your mango; you can eat it quite safely, if you just wait a moment while I enchant it so that it won't splash over you.'
Quite a short spell and a little wiggling of his wand were enough, and then I ate the mango. It was wonderful. It was the only fruit I have ever eaten that was better than the best strawberries. I can't describe the flavour, which is a mixture of all sorts of things, including a little resin, like the smell of a pine forest in summer. There is a huge flattish stone in the middle, too big to get into your mouth, and all round it a squashy yellow pulp. To test the spell I tried to spill some down my waistcoat, but it merely jumped up into my mouth. Mr Leakey ate a pear, and gave me the other five mangoes to take home. But I had to eat them in my bath because they weren't enchanted.
The anecdote about the suitcases is in the third story, "Mr. Leakey's Party":
'This is Mr Dobbs, the physicist,' he went on, as he introduced me to a short fat man with a red face and no hair on the top of his head but lots on his chin. 'At least he was a physicist, but he's out of work now. He used to make £3,000 a year out of the railways by travelling with excess luggage.'
'I beg your pardon.'
'Excess luggage. Ordinary people have to pay for theirs, but the railway had to pay to carry his, because it weighed less than nothing, like a balloon. Mr Dobbs had some special bags. When he put them on the weighing machine at the station he pressed a button which opened a thing like a sparklet inside, and let out hydrogen into the bag, so that it pulled upwards, like a balloon.'
'But why didn't it fly up into the air?'
'Ah, that's where Mr Dobbs was clever. The gas coming out of the sparklet thing worked an electromagnet which pulled up the iron floor of the weighing machine. So they had to pile on weights to make the machine register nothing. You see, if your bag weighs a hundredweight more than it ought to you have to pay the railway company, but if it weighs a hundredweight less than nothing, they have to pay you. ...
The collection is in the public domain in Canada and can be read at Project Gutenberg Canada.