Like Phil I prefer sketching out plans, as somehow track plans are very "organic", so I have simply inked over my sketches and scanned them in. I use squared paper and in this case 3cm to 1 foot, or 2" to each square. I've allowed for point lengths and clearances but these plans are just approximate, for any micro layout a full-size plan would be a great idea, using the Peco point templates (send them an SAE!) and actual stock to check clearances. You can even use boxes and card cut-outs to check buildings fit and appearance.
Phil mentioned an Inglenook, which is a minimal shunting plan with 3 sidings, and often used as a puzzle. However to fit this plan I've used the reduced size with sidings for 2-2-and-3 wagons, and a headshunt for a loco+2 wagons. Even then I've suggested wye points to save space! I've sketched an industrial scene, the gate to the front left might lead across a road to the main railway yards. This system might be operated by small industrial locos, and for interest there is a small engine shed, although operationally it does not really feature.
The next plan features a full-size inglenook, for 3, 3, and 5 wagons. However to achieve this an external fiddle yard is required, but that would rather defeat the point of building the layout in the box Phil has! So my idea is to hinge the yard such that it folds over the layout, when open a bridge could easily hide the hinge pillars. Using cassettes would allow the fiddle yard framing to be on top of the deck, saving height when folded into the box.
I've added a kick-back siding again but this time run it under the bridge to suggest the end of a run-round loop, adding a little operational interest. Indeed a small platform could be squeezed in, OK a station is unlikely but perhaps an internal system running works passenger trains would be plausible, maybe a naval base?
Another good basis for a micro layout is a locomotive depot, after all you're never going to run much in the way of a train in 73cm but if you like locos (and who doesn't?) this gives a great excuse to show off your collection without bothering with stock! This plan is a rather small depot, and like my Southon Yard 009 loco depot only the front of the shed is depicted (we want to park the locos on show!). I've used a coaling stage to hide the exit track, but if that seems a bit grand a works building of some kind would do - a wagon repair shop if you like wagons.
However despite using a 3-way point, to allow reasonable space for locos on display there isn't really space for a fiddle yard, even though all that is required is a cassette for a loco. In fact the Peco Loco Lift would work a treat, even if just the end rests on the lead track. To support the other end of the cassette or loco lift perhaps the end of the baseboard could incorporate a telescopic or hinged arm!
The final plan takes on another aspect altogether. Phil wants somewhere to pose locos and stock for photographs, which brought to mind those ex-works photographs seen in books where the new loco is posed on the works traverser ... hmm, how about a model works traverser! This plan is completely pointless (!) and features the traverser at the centre. Making it work could be a challenge! To the left are sidings to pose locos and stock outside the repair shops, for added interest the back siding could be the goods inwards loading dock. For a fiddle yard the same cassette system as the last plan is used, hidden by the erecting shop and a raised walkway.