What kind of magic items are appropriate to a swashbuckling & sorcery campaign, particularly given the kinds of character classes available?
Of the non-spellcasting classes, duelists, bandits, and mariners are all treated as fighters for purposes of magic items available, subject to the individual class restrictions for armor and weapons. The entertainer is treated as a thief but may not cast spells from scrolls.
Of the spellcasting classes, availability varies much more. The witch and the cloistered cleric are treated as a magic-users and clerics, respectively, for purposes of magic items, though the range of weapons and armor is limited for the cloistered cleric. The alchemist has a number of unique restrictions regarding magic items.
Taking a look at the magic items tables in the 1e AD&D Dungeon Masters Guide, potions seem like a good fit for swashbuckling & sorcery campaign, particularly given the presence of the alchemist class. A potion of climbing and a philter of love seems like a potent combination for illicit romance.
Scroll use is as per the equivalent base class, with the exception of the entertainer, who cannot cast spells from scrolls like the thief, and the alchemist, who cannot use scrolls at all.
Rings are another good fit for swashbuckling & sorcery magic, and all of the classes may use rings not prescribed to a particular class (q.v., ring of wizardry).
Rods may resemble a fencing master's baton when carried by a duelist, while staves and wands are used by witches without restriction.
Among the many miscellaneous magic items available in the DMG, a few stand out as particularly appropriate for a swashbuckling & sorcery campaign. The alchemy jug and the beaker of plentiful potions will be highly prized by alchemists, while bracers of defense and cloaks of protection and displacement will be highly sought-after by the lightly-armored fighting classes as readily as the entertainer or spellcasters - but perhaps the code duello of the campaign world prohibits the wearing of magical items of defense during a duel? The broom of flying is a natural item in a campaign with witches.
The various helms, on the other hand, are likely less common - perhaps broad-brimmed hats receive enchantments instead? Javelins, nets, and tridents are rare except among seafarers.
In fact, whereas most of the other magic items can be used pretty much as written, magic weapons and armor are perhaps the most problematic without significant changes to the existing tables. Rather than short- and longswords or bastard swords, basket-hilted broadswords, rapiers (using stats from A Mighty Fortress for 2e AD&D), scimitars (as sabres and cutlasses), and even two-handed swords will make up the bulk of magical personal weaponry.
War hammers and polearms of all sorts, crossbows and bows, hand axes (particularly among mariners), and daggers remain, but maces and battle axes are rare or non-existant. Magical firearms and ammunition, again borrowed from A Mighty Fortress, might have a place in some swashbucking & sorcery campaigns as well.
Magical armor may be present but given that, with the exception of the mariner and the bandit, metal armor cannot be worn, it should likely be rare, with the aforementioned cloaks and rings of protection being more common.
In general, magic items in swashbuckling & sorcery should be selected based on genre appropriateness, and some unique, campaign-specific items - a magic fan which becomes a buckler, perhaps, or a magic cloak, which when wrapped around the forearm acts as a shield, or a mouchoir (scented handkerchief) which acts like a potion when inhaled - added.
Y'know, this could actually turn into a thing . . .