A bike with some lights, everything else is optional.

I have the same, and I use the Kona Minute Cargo bike most of the time.

But I also do it on the full carbon road bike, or the Langster singlespeed too

TBH you could do it on a bmx, I just find the Cargo to be the nicest day to day, and the most use if I need to pick anything up on the way home

My commute used to be 5 miles, I did it on a ’93 Cindercone with mudguards, rack, panniers, and lots of lights. Don’t get anything too fancy as a) it might get pinched and b) you want something heavy to make the 5 miles worthwhile! I used to carry way more than I needed in panniers just to make things a little more challenging 🙂

I do 18 miles each way and prefer a sweaty back to a bike that handles like a pig. I have a rack and panniers. Hanging up in my garage. Try both and see what suits you.

Lights- and some back ups if you are commuting when its dark (I work shifts so a least one of my journeys is fully in the dark).

Might sound like I’m trolling but I think that some people go out expecting conflict and therefore find it (anyone that rides with a helmet cam to capture road rage for instance). I see more considerate driving than in considerate, and I believe in positive feedback not negative. If I see someone has waited for me to pass before pulling out/turning/opening door etc I’ll give them a big wave and a thank you as I pass. If they cut it close what good does giving them the finger achieve, its going to make them more antagonistic towards cyclists not give them cause to calmly reflect on their driving.

sharp elbows and thunderous thighs.
mmmmm, thighs.

This is my bike: 3-speed hub-gear with coaster brake, roller front brake, enclosed chain with Hebi chainglide, Schwalbe marathon-plus tyres, dynamo, saddlebag, full length mudguard.

I’ve oiled the chain a handful of times this year!

you’re spelling it wrong.
:tee hee:

this is what happens when work springs an offshore trip on you with no notice :d

A reliable bike – noting flashy (except the lights, ha!), just reliable and comfy. A 4 mile walk because your unloved chain exploded is a PITA.

Lights, many thereof. Good to have 2nd front and rear ones in case the main ones give up the ghost.

Mudguards. They reduce the misery of splashing through puddles of god-knows-what slightly more bearable.

Waterproofs if it’s raining (or looks like it might). 5 miles might not be far in the grand scheme of things, but even if you’re only out in the pissing rain for 20mins it’s still nicer with a jacket/trousers that keep you dry, especially if you’re not going flat out, so aren’t going to get too sweaty. 🙂

Good clothes, mudguards and lights.

Anything to minimise faff is a good thing IMO too. I.e. bolt up / non-QR hubs so you don’t need a separate cable lock, lights that are permanently-attached and don’t need removing every time you leave your bike unattended.

As others have said, I don’t find panniers to be especially amazing. The extra weight over a rucksack is significant and for my 6 mile commute, having the weight over my shoulders isn’t a problem. I actually use a pannier now – I bought it to see if I liked it and it’s stayed on my bike mainly out of laziness TBH. YMMV

Schwalbe Marathons or Marathon pluses too – they are VERY good tyres!

breakfast.
post ride breakfast.
spare pants/socks left at work

I have had this – at least I had the rain kit. Missing links and a chain breaker are now in my commuting kit.

If you’ve an unlit stretch, a head torch (Alpkit gamma etc) makes puncture repair/tube swapping a bit easier, and can be an emergency front light or just provide extra visibility at junctions.

Tools: I don’t bother with any tools or anything. It’s 3 or 4km, I’ll get to work quicker if I either walk the rest of the way or head home and ride a different bike in.

For getting home, I have other options I can use, or just walk it pushing the bike.

Speaking of which: multiple bikes is useful. I generally don’t have time (or energy) mid-week to repair things, so just ride a different bike until the weekend 🙂