I Need Grocery List Advice

tomatoes basil garlic olive oil eggs milk cheese pepper and meat

Fresh fruit and veg - whatever's in season or on offer. Spinach, mushrooms, onions, peppers, tomatoes are my must haves.

Dairy - semi skimmed milk, natural greek yoghurt, cottage cheese, eggs.

Meat and fish - chicken breasts, lean steaks, fresh fish. I also usually keep some frozen raw prawn/ shrimp in the freezer at all times.

Tins - tinned tomatoes, beans (any variety, red kidney, borlotti, cannelini). Tinned goods will be high in sodium, though.

Bread - I only eat bread every few days, so I buy a good quality seeded sliced loaf and keep it in the freezer - toast one slice from frozen when required.

I'm thinking you're looking for staple ingredients since you said "once a month" type shopping... so here goes!

Spices- they change any staple food cinnamon, nutmeg, ginger etc in smoothies flavor spices for meats or other dishes

Frozen berries and veggies. They are easy to fix and add to things

Eggs (can last up to 5 weeks, check the date)

Mixed nuts (or your favorite nuts)

Protein powder

Coffee (if you drink it)

water (if you need to buy it)

popcorn kernels (for homemade popcorn)

olive oil

meats (you can freeze it in portions if you find good sales!)

plastic sandwich/snack bags and storage containers (These help me prep my weekly meals and snacks)

beans (canned or dry, you pick) add to main dishes or salads

dave's killer seed bread (light) I keep it in the freezer and use as needed

apples and lemons (they last several weeks in the fridge!) They have a variety of uses! Lemons add flavor to water, fish, salad,
marinades, etc and if you find they are getting soft and need to be used, you can clean with them, or add a couple drops of honey to a half a lemon (or smaller) and use as a facial. Tons of other uses for lemons!
Apples can go in salads, with dips, eaten whole, sprinkled with cinnamon, applesauce and they are easy to transport or grab for a quick snack! chop an apple, put a half teaspoon of salt in a bowl of water and soak the apple for a minute. It won't turn brown!

I can't think of any thing else off the top of my head... those are my "must have" items.

I could not imagine shopping once a month I am a fresh veggie eater so split up my list each week Planning a menu helps
I start at the produce section luttuce, tomatoes, onions potatoes some times fresh green beans, or sugar snap peas, bean sprouts (thinking stir fry) brocoli green peppers carrots avacados and one fruit.. go to the meat section frozen talapi,lean hamburger (I divide it up in meals, pork roast, and chicken, and sometimes turkey that goes for several meals)bread then dairy/eggs //cheese those are all on the outside isles then for the inside shopping comes cereal rice/beans tomato sauce and spices coffee.. I buy spices to add to my collection of chili powder ,garden garlic powder, oregano,cinn,collander,mrs dash, salt pepper,chives catshup/mustard and mayos coconut oil,sesame oil or olive oil once bought last forever,.
The simplier and whole foods you buy the healthier it is. I would say the veggies and meat take up most my cart. If I go to the inside isles I am too tempted to pick up junk like chips and cookies..When I go by thoses sections I say to myself "You don't need those you have flour and sugar at home and can make it if you really want it... same with pasta..
I buy a few cans of canned green beans or beets salsa condiments like pickles and such last awhile, but the first initial buy is expensive..kinda got to build up by buying canned goods when on sale.

I've gotten to the point that I only shop the outiskirts of the grocery store. Fresh, lean cuts of meat, fresh fruits and veggies.... the only things I go into the aisles for are brown rice or whole wheat spaghetti (and the household items). Nothing canned, nothing boxed.... fresh is best. And if you can't get fresh veggies, get frozen.

In my house:

12 grain bread
Skim Milk
Eggs
Brown Rice
An assortment of Veggies, whatever looks good or is on sale but ALWAYS baby spinach, red peppers, carrots and mushrooms