It has always been a fundamental part of being a man that you must be able to carry all your day-to-day essentials in a small piece of folded leather that slips neatly into your inside pocket.
Everything you're likely to need will live in there including methods of paying for stuff, old receipts that you can no longer remember what they were for, and in my case the occasional moth.
Keys are about the only thing it's permissable to carry separately, and these should ideally be shoved into your trouser pocket in such a way that they stab you in the leg when you sit down.
The reality, however, is that we often need to carry more than that, and this leads us to a whole minefield of problems.
My wallet only ever contains cash on the day I'm due to buy my weekly bus ticket, but it does do a pretty good job of ensuring an assortment of cards including payment cards, driving license, organ donor card etc, are kept in one safe place, but it lacks the capacity for other things I need to carry most days.
The wife carries a bag that I call 'Bessie' (a reference to Courtney Cox's bag in the comedy series 'Cougar Town') which is roughly the size and weight of a small country. I avoid getting too near it for fear of getting lost, but it seems to contain anything and everything you might need and plenty more that you won't.
Hermione Granger had the best bag ever in Harry Potter, which was physically the size of a small handbag but had immense capacity. Unfortunately my lack of magical powers means that such a thing is not an option, so I'll move on.
On the average weekday I'll travel to work with a small rucksack over one shoulder that contains a decent size lunch box, a pair of full-size Sennheiser headphones, an iPod Nano, keys and ID card for work, and usually a packet of ibuprofen.
The trouble with this is that anyone carrying a rucksack in Cambridge is automatically assumed to be a tourist, and for many reasons outlined in the previous post I'd prefer to avoid that association.
So what's the alternative?
There are sports bags which are fine if you're going to the gym or to play squash, but otherwise they're too big and cumbersome.
A briefcase makes anyone other than a lawyer or estate agent look like a dickhead, and those people generally achieve that without one.
What you're left with is that relatively recent fashion item - the man bag.
Most of these are along the lines of what I understand are known as messenger bags, but as usual life becomes increasingly complicated the more you look into it.
I've looked in lots of shops and on various websites, and while the variety of options is mindboggling, I have at least been able to narrow down the field a bit.
I don't want one of those that looks like your stereotypical professor bag - you know the sort, brown leather with a fold over front secured by two buckles, and a single handle on the top.
In fact I don't want it secured by buckles at all because they're time consuming, and none of those plastic spring clip things either because I'm guaranteed to end up with fingers covered in blood blisters where I've got them trapped. Velcro is cheap, nasty and noisy, so that leaves either a zip or maybe those little magnetic button things.
The ideal bag will be big enough to accommodate the items mentioned above, but not so big that it's clumsy and awkward to carry on the bus. Waterproof would be good, and a shoulder strap rather than a small handle. It mustn't be bling, shiny, have big corporate logos on or look 'a bit gay'. I don't care if someone is, but I'm not so I don't want to give that impression.
So what to do? I guess the right thing will present itself at some point and I'll just have to get it when it does - otherwise I'll never see it again. Of course sods law dictates that when I do see the right one it'll have a silly price tag attached, so I'll walk away shaking my head and tutting, telling myself I'd rather keep the rucksack and risk being mistaken for a tourist than be ripped off over something that is essentially lunch box camouflage.