Here's some things on my keto shopping list:
- Greek yoghurt (10% fat - important it is Greek, look for <4g/100g carb content)
- Peanuts (important to check, should be ~7g/100g carbs, some have flavours that add significantly)
- Almonds/Hazelnuts/Macadamias/Walnuts; avoid cashews (~20% carbs!) and pistachios
- Raspberries or blackberries
- tuna mayo
- Boiled eggs
- most cheeses
- double cream for coffee as a treat
- Prawns/smoked fish
- Salami (check some as a few have carbs added, avoid meatballs and similar as often 10% carbs)
- cut meats
- pork scratchings/chicken skins
- avocados
- bacon
- meats/fish
Obviously many of these you cannot buy off the shelf, but some pre-cooked options you can find in places more frequently now (cooked meats/smoked fish; boiled eggs, etc)