Out-Dated-Knife

piping bags:

if you've seen any sort of decorating hacks, you've probably seen that trick where you cut off the corner of a ziplock bag and use that as a piping bag. that's fine if you're just doing like a drizzle on something, but those burst easy so they're a pain to try and use for a full cake or for a batch of cupcakes.

you can also get cheap piping bags with the tips already cut off. they're usually in the baking aisle at grocery stores where they have sprinkles and stuff, and they usually come with a few tips as well. those are fine if you're going to decorate one cake and then never do it again, but those also sometimes burst easy depending on the brand, and the price per bag is not very good.

I'd recommend getting a roll of pastry bags. these are the ones we use at work. one roll of these lasts us a few weeks at the store, so if you're only making a few birthday cakes a year, one box will probably last you at least a decade or two. I'd recommend getting the 18" size. 12" is fine for doing a single cake, but is a pain to constantly refill if you're doing cupcakes, and 21" is kind of overkill for anything you'd be doing at home.

couplers:

these aren't strictly necessary, but they're nice to have. they allow you to swap out your piping tip so you can keep using the same colour of icing with a different tip without having to get a new piping bag.

these are fine to cheap out on, but make sure to get ones that don't have a notch in them! the ones without a notch can double as extra wide round tips

you want to get "standard size" couplers. those are the ones that fit the smallest/"regular" size piping tips. they do make bigger couplers for bigger tips, but even though I decorate cakes nearly every day, I've never felt the need to use them, and the cases where I could use them are pretty niche. don't bother with bigger ones unless you have a specific reason that you want to get them.

also, when you're cutting your piping bag to fit your coupler, you want to make sure the hole is big enough that it doesn't cover the opening at all, but small enough that it does cover the threads so it doesn't slip out while you're piping (unless you have really tight couplers, but in my experience they usually screw on a bit loose to account for a piping bag being in the grooves). the big piece goes inside the bag, then the tip goes on top outside the bag, then the ring slips over the tip and screws on to keep it in place.

cake combs:

probably the least necessary thing on this list, but they're fun. they take a bit of practice, but basically you just run them along the sides of your cake to add texture. just get the cheapest variety pack you can find. also, having a flat-edged cake comb will make it much easier to get clean, smooth sides than trying to do that with your spatula.

also if you're going to use cake combs, you'll probably also want to get cake boards. they make disposable ones and reusable ones. just get the boards you like. the main thing is that cake boards are flat, but plates have a lip around the edge. if your cake is on a plate, that lip is going to get in your way if you try to use a cake comb.

offset spatulas:

another thing that's not strictly necessary, but will make your life easier. I like to use a bigger one for the top of the cake, and a smaller one for smoothing out little details if I'm drawing something. the angle just makes it easier to smooth stuff without your knuckles getting in your cake

piping tips:

there's a million billion different types of piping tips out there, but most of them you'll hardly ever use, and a lot of the cheap tip sets are full of those useless tips. they go for maximum variety when it's usually more useful to have a bunch of basic tips in different sizes. this is the set I bought for myself if you just want to get a set and be done with it, but I'm still going to go into the different types of tips.

these aren't all the tips that I use regularly, but I think of these as like the 5 "main" types of tips. if you have these, you can do most standard cake design things.

round tips:

pretty self-explanatory. good for writing and drawing.

star tips:

these come in a bunch of different shapes and sizes, some with longer or shorter spikes, or different numbers of spikes. they all give similar but slightly different looks, and it's mostly up to personal taste what you like best. the main thing to look out for is "open tip" vs "closed tip". on open star tips, the spikes stay straight, leaving a wide open space for the icing to flow through, while on closed star tips, the spikes curve inwards, leaving a tighter space. if you can only afford a few, I'd recommend getting open star tips. they're more forgiving of wobbly hands, and they're less likely to get clogged if your icing isn't perfectly mixed.

for a real classic-looking cupcake, you'll want one of those jumbo size star tips. like the kind you can fit your thumb inside. most basic tips come in these jumbo sizes, but star tips are the most useful at that size.

petal tips:

petal tips are wider on one side and come to a point on the other. sometimes they have a bit of a C or S curve to them, but I only ever really use the straight ones. most flowers are made with these, the pointy side making the edge of the petals.

it's a good idea to pick up a rose nail if you want to use these. you make the flower on the rose nail so you can have better control and don't have to worry about smearing your cake by accident. you either use scissors to transfer your flower to the cake (harder to do, but faster), or pop your flowers in the freezer so they become solid and you can just pick them up and place them. there are a bunch of flowers you can make with these tips, just look up some tutorials for buttercream flowers.

they're also good for doing ruffles, like what I did along the bottom of this cake.

leaf tips:

these guys make leaves. there are two main types of leaf tips, that "M" shaped one, and the "V" shaped one.

personally I find the V one easier to use, but also you can just cut a little V out of a piping bag and it'll work almost as good.

the M one is also good for doing ruffles, like the blue drape-y parts on this same cake again.

grass tip:

it makes grass. also fur.

russian piping tips: