I'm still working my way through 'knowing' the products available at Japanese grocery stores.

Many of them, such as Soy/Shoyu, Mirin, Hon no dashi/concentrated dashi stock are catalogued and explained in reputable recipe books.

But then there are other, unexpected treats. Packets and potions that you don't pick up because you're not quite sure what to do with them.

If anyone does decide to contribute, I'd be grateful if they could indicate by (v), (f) or (m) if they believe the product is vegetarian, contains fish, or contains meat.

My tips include:

Panko - Breadcrumbs (v). Until you try them, its hard to explain why they are so superior to other kinds of breadcrumbs. My real tip is to use them for other dishes - namely pasta - as a delicious, light tasting crispy topping. Heat some olive oil, heat some garlic, but only for a moment, and add the panko, perhaps with some rosemary or thyme. Fry the panko until lightly golden coloured and use as a topping (same way as you would grated cheese). Once opened, I tend to keep panko in the freezer. Also great as a coating on European style fishcakes or mashed cannelini and cheese 'burgers'.

Shiso flake seasoning for rice (v). A kind of furikake. I like the yukari brand.
Purple powdery stuff in a packet (ask for shiso gohan) you add it to freshly cooked rice to give it slightly sour fragrant flavour.
I also add a tablespoon of shiso gohan to mashed pickled beetroot and combine with dressings (either mayonnaise with/or a little sour cream/creme fraiche and a touch of yoghurt perhaps, or oil) to make a vibrant pink sauce to go with salad, new potatoes and breaded fish. (If I have an ume boshi/pickled plum I mash one or two of those in as well, the beetroot was originally used as a substitute, but we found we really liked it).

Cooking with 'hon no dashi' (f)
These come in bottles labelled "Tsuyu" (or tsuyu soup stock in English)
As well as soups and dipping sauces, I make garlic rice with them.
Have some cooked rice ready, heat some oil in a pan or wok, and lightly fry two or three sliced cloves of garlic. Add the rice, stir quickly to coat the rice in oil, and push the rice to the side of the pan. Pour in a table spoon or two of undiluted dashi stock and push the rice on the other side of the pan to the side and do the same there (this is so the stock heats up), very quickly stir everything together and take off the heat. The rice should be slightly darker now. If you have fresh shiso leaves, use them, otherwise combine plenty of fresh basil and mint leaves and chop/shred them together and stir these through the rice. The basil and mint was originally meant as a substitute, but we really like them and will still use basil and mint even when we have shiso. The three herbs combine very well. You can add shiso gohan instead if you haven't got shiso and still want the particular fragrance it brings
The chicken stock recommended by valvebouncer below, is often used to flavour rice in Japan the way I use the hon no dashi.

Recently discovered:
Hiyashi Ramen or Hiyashi chuka (f) - easy to make a (v) version yourself:
http://japanesefood.about.com/od/noo...yashichuka.htm
Wish I'd discovered it earlier this summer!
I bought it thinking it was a Japanese style noodle bibimbap.
I got the Toyo Suisan brand for under $1. We had two packets each with the following:
Julienned cucumber (did this first and left in a colander with plenty of salt - rinse out the salt and drain after 20 minutes)
A quick omelette (adding a dash of dashi and mirin - or soy sauce and sugar to the beaten eggs)- cut into fine strips
sliced tomato
sauted julienned zuchinni/courgette
some crab sticks we had in the freezer - stripped into floss
Boil the noodles for 4 minutes - rinse with cold water until cold and drain.
Put noodles in bowl - add dressing and sesame, put on toppings.
The 'japanesefood' link gives more ideas.
All the websites say don't use instant noodles for this dish, but these were really good.