Sump plug is 12mm... not usually part of an Allen key set, but usually in those relatively-expensive 1/2" drive sockets that have Allen key 'stubs' permanently fitted. 'jjhepburn' bought me a top-quality metal box of those for my birthday and although at first it seemed of limited use (I already had a 12mm Allen key

) they have turned out to be worth their weight in gold, easily the most useful gift I've received in a long time

Useful for all sorts of jobs on cars other than the Uno (come to think of it, essential for getting the driveshaft joints apart on the Uno Turbo...)
Like Beau, I remember the floor and sill starting to crumple on one rusty Uno when I used the original jack

I think it's worth having a trolley jack, safer really.
Jacking up the Uno can be a bit awkward because the strongest place to put the axle stands (under the curved 'saddle' of the suspension arm rear clamps) also happens to be where you want to put a trolley jack. The next best place is the 'jacking points' (which aren't really jacking points) in the front floors - a double-thickness piece with a round hole - which is where you want to use a trolley jack. That doesn't leave much space to get the axle stand in.
If you have a big enough trolley jack - has to be bigger than the small ones, real workshop-size 2tonne plus - you can place that under the clutch bellhousing, at the join between the engine and transmission (as shown in the handbook), then raise the car with speed and ease (it will be unbalanced, as the jack is off-centre), and then place the stands under the suspension arm clamps. The bigger the jack, the better for this, because when you lower a jack that's near the end of its capacity, the car tends to move backwards and misses the stands. You know how well the Uno handbrake usually works, so you could also chock the rear wheels. The other problem is that the bigger jacks won't fit under a lowered Uno. Jacking up my Turbo has now become a bit of a fiddle since I bought a big new trolley jack - I have to use the car's own jack to raise it a bit first
Never be tempted to use two of the car's own jack, one each side (I think you'd work that out pretty quickly...) jjhepburn and I operated one jack each side... his side went up faster and the Uno lunged towards me as the jacks folded... we laughed and laughed

I guess it makes a fun game... the winner is the one who manages to get the Uno to lunge towards the other person... Oh forget I said that, health and safety etc.
Seriously, I think it's best to ALWAYS assume that the jack you're using, whatever the type, is about to collapse! That means keeping clear of the car as you raise it...
-Alex