If you cast Mage Hand on a 1 lb non-magical saucer, you can float it around, right? What if there is a 1 lb teacup on the saucer? Can you still move the saucer around, with the teacup? What if a 2 lb kitten is on the saucer? What if the kitten is wearing a magic item?
Now, the Mage Hand cantrip is very limited ... it can only lift "one nonmagical, unattended object weighing up to 5 lbs." And arguably, a saucer with a kitten on it or a fortress box with a reduced halfling in it is attended (by the kitten or the halfling). So Mage Hand seems out, if you are interpreting "attended" very strictly. Still, nothing says you cannot research a first level "Improved Mage Hand" spell that let's you move attended and magical objects, but is otherwise exactly the same.
Say you're an average female halfling, which by Core RAW means you are 2 ft 11 in tall and you weigh 30 lbs. You cast Reduce Person on yourself, so that you are now 1 ft 5.5 in tall and you weigh 3 lb 10 oz (Tiny size). If you sit on the saucer, can you Mage Hand it around, in essence riding your flying saucer as if it were a flying carpet with a move of 15 and requiring concetration?
Could you cast Unseen Servant and have your Servant carry you around? How high off the ground can it lift you?
What if, while you are reduced, you use Disguise Self to make yourself appear one foot shorter? Now you appear to be 5.5 inches tall -- Diminutive size, or maybe even Fine. Can you accrue any of the modifiers for being Diminutive or Fine? A Tiny creature has a +8 on Stealth checks, and a Diminutive one has a +12 … would you grant a bonus to Stealth to the 5.5-inch-seeming reduced halfling? [How about a bonus to stealth if you are also floating around with a Mage Hand? That's gotta be pretty quiet.]
a strict reading of the RAW would allow an 11-inch caster to appear 0 inches tall, but not invisible. Kind of like a shadow, say, or a pancake, IMSNHO.
A DM could certainly house rule an applied scaling or proportionality for Disguise Self, instead, but that would be a house rule.
Of course, following a strict RAW approach, there is also zero reason to argue that the spell can ever give a numeric bonus to anything beyond disguise checks, regardless of apparent size. Thus making yourself seem super small (or two-dimensional) is a strictly RP application, or maybe useful if you are using disguise to appear as an inhabitant of a Flatland-like plane. :-) Or if you seek a disguise as an ink blot, say, or a work of abstract art. :-)
Say you make or buy a Mithril or Darkwood box with airholes on all sides that weighs 10 lbs. Say you are a reduced female halfling weighing 3 lb 10 oz. Your Unseen Servant can carry 20 lbs. Can you hop in the box, gaining the benefit of improved cover, and let your Servant carry you around? While you cast spells and fire teensy crossbow bolts from inside through the airholes? Since you have improved cover in your box, you are immune to AoOs and can make Stealth checks in there, right? You can even snipe from in there, right?
At low levels especially, the Unseen Servant is a goodie -- it has no AC and cannot be attacked, and it provokes no AoOs. As soon as you take area / energy damage, however, bye bye. But at higher levels you can get an Improved Familiar to carry your fortress box around for you. A Small Air Elemental would likely serve just fine! Just have feather fall prepped for when you are dropped.
Oh, and Unseen Servants can walk on water ... and wooden fortress boxes can float!
There are also options for Animal Companions and Improved Familiars to carry your fortress box around for you.
This screed was posted here on 4 Aug 2014, but it was mostly written as a message board post on 17 Jan 2013.