I have a can of mackerel in the cupboard, and some potatoes that should probably be used. I have an onion. There are eggs. Let’s see… There’s a jar of parsley flakes, there might be some usable cilantro in the fridge, I have garlic, and a bunch of spices.
What I don’t have is any experience making fish cakes. How 'bout some recipes? 
Stir 1 egg into 1/3 cup mayo. Add chopped fish, seasonings, and dry bread crumbs or moist breadcrumbs. For dry bread crumbs use about 1/2 the volume of the fish. For moist use the same volume. Fold the mayo mix into the other ingredients so you don’t turn the fish to mush. Make patties and fry about 5 minutes on a side, or bake in oven for about 20 minutes.
I suggest adding some dill, and some peppers. Top with tartar sauce or remoulade, or just about anything. Make the potatoes separately. You could cut slices of potato, fry them along with the cakes, and top each cake with a potato slice.
I was under the assumption that mashed potatoes were mixed into the fish. I do have dry bread crumbs in the cupboard.
I also have dill. Alas, it’s dried. (Hm… I also have a tube of dill paste in the fridge. Not as good as freshly-chopped, though.)
Almost out of mayonnaise. It’s listed on the whiteboard on the fridge.
Mackerel might be a bit too oily(IMO) I use mashed potatoes , flaked fish( ie salmon, cod etc) parsley, seasonings, Old Bay is good, egg, add some bread crumbs to firm up mix. Roll in panko shallow fry.
Salmon is also an oily fish, and it’s used to make fish cakes. I think (having never made fish cakes) mackerel should be fine. (And it’s what I have. 
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Mmmmm, man I ate a lot of mackerel cakes when I was a kid. Cheap food And so fun to crunch the bones!
Dill is one of those herbs that is excellent in its dried state and maintains its potency. I would also recommend thyme as an alternative.
I’ve had fishcakes where instant mashed potatoes were mixed in and I didn’t like them. If you make real mashed it might work out, or cook them a little less and add them in diced.
IME, it’s nowhere near as potent as fresh. But it works when it’s all you have.
OK, here’s what I’m thinking…
A can of mackerel, drained. One egg. One-half the amount of mackerel in bread crumbs. Some minced onion, dried parsley, dried dill, and Old Bay. A couple/three tablespoons of mayonnaise. Shape into patties and fry in oil. Mix up some aioli/tartar sauce/remoulade for a sauce.
Daijoubu desu ka?
If you don’t mind the smoke you could use the Old Bay as a blackening spice. Just coat the cakes with melted butter and apply a good layer of Old Bay, fry on a dry skillet.
Also, let the cakes sit in the fridge for an hour or more before cooking to firm up.
ETA: And I agree with Chefguy, dill is a spice that’s still plenty good dried.
Ichiban, tomodachi.
For a while, I delivered The British Weekly and L.A. Rock Review. I used to drive by a place in downtown L.A. called Ono Fish Cakes. (They made the Japanese style, and not what we’re talking about here.) I couldn’t help but say ‘Oh, no! Fishcaaaaaakes!’ every time.
They turned out well. Especially since the mackerel came from Dollar Store.
I love thoses wacky dollar store canned food labels.