What I use on a daily basis:

Reg Barber tamper, Bumper tamper holder
Any decent tamper will do. I like having the tamper holder because I keep the tamper on a shelf above the machine, and it's much cleaner with all the coffee residue kept in the rubber base where it can be rinsed easily.

Motta knock box
You can get by without a knock box, but it is quite useful. You really need the padded bar to give the portafilter the appropriate whack to knock out a puck cleanly. I suppose you could DIY something if they are too expensive. Either way, don't get a tiny one unless you want to dump it frequently.

12oz steaming pitcher, 20oz steaming pitcher
It's very useful to have both sizes available. I have several 12oz pitchers so I can just fill them up at the beginning and bang out milk drinks without having to pour milk for every drink, but it's not exactly necessary.

0.1g resolution scale
Extremely useful for checking your dosing consistency to eliminate it as a problem or use it as a variable to modify your shots. This scale is a favourite. It runs on AAAs (easy to replace) and is compact and accurate enough. I've tried a couple of other scales, but neither held up as well when covered with coffee grounds and the occasional espresso spill.

Bottomless portafilter
Seriously, just do it. It's invaluable for fixing extraction problems, especially as a newbie. Plus it makes your espresso shots look pretty.

Group brush
I have a Pallo Coffee Tool, but I'd like to get a Cafelat Group Cleaning Brush. Doing a portafilter wiggle gets almost everything off the shower screen, but it's good to scrub the gasket area now and then, and it's also good to brush the block above the shower screen while it's off for cleaning periodically.

Cafelat corner tamping mat
Any piece of rubber will do. I've also used folded up dish towels. I prefer to tamp on the edge of the counter, and some bottomless portafilters are cut so this is required, so I like the corner tamping mat specifically. I'd consider a tamping stand if I used a spouted portafilter regularly, and it's kind of required for single spouts.

Grinder brush
It's always handy to have a brush for your grinder. You can probably find something good at any art place, but a lot of espresso dealers carry brushes in an appropriate shape for not too much. Some people also like a large brush for keeping the counter clean. Whether you need either brush will depend on your grinder.

Lots of bar towels or microfibre cloths
You go through these like crazy, especially because anything you wipe out the portafilter basket with has to be dry. I usually keep one damp one for general wiping (PF baskets with lots of grinds stuck in them, steam wands, etc.), and one dry one. I just rotate through a drawer of bar towels.

Lots of cups
I like ACF cups, but anything will work. You don't want to have to keep cleaning the same two cups over and over again, so buy a few.


What I use less frequently:

Espresso machine detergent
I backflush my Duetto with Cafiza every couple of weeks, and I soak the portafilter, baskets, shower screen, steam wand tip, etc. It also cleans the inside of my travel mug beautifully.

Descaling solution
Either a commercial mix or something like citric acid. You shouldn't have to do this very often, so it's not necessary to buy it up front. I use Dezcal.