Assume you had access to a 6 by 6 balcony that faces south with a nice railing and (miraculously) endless access to water. Set whatever budget makes it interesting for you. How would you design your garden to produce as much food as possible? Could you produce enough to sustain yourself? How close could you get? What crops would you prioritize?
Potatoes grow well in grow bags, so if you have a spare corner without a planter, throw one there and you get a decent yield. My only complaint is they have a pretty long grow time so it’s a single crop.
Lettuce is great because it grows fast and you can reseed several times a season. Tomatoes are great, too, and better than what you’ll find in a store. Long harvest period, too.
Honestly, having gone down this road for a few years with mixed success, I would say plant the things you actually like to cook and eat. High yield foods are great but if you aren’t passionate about the plant, you won’t be excited when you harvest it.
If you have limited space, quality compost ensures you get the most bang for your buck, it makes a huge difference. The best results I’ve had have been for potatoes, peppers, tomato, radish and the best compost was from our community composting bin (yes, made from our pooled veg scraps).
The amount of food you can grow using Square Foot Gardening in a space that size is surprising! Follow Square Foot Garden methodologies using 12” pots on floor, trellises/netting along walls, and hanging planter boxes on railings. Pots are filled with tomatoes, potatoes, onions, peppers, etc. trellises are beans, cucumbers, squash, melons, etc. Hanging planter boxes are filled with lettuce, spinach, kale, carrots, etc.
I go through so much broccoli, onions, and mushrooms so I’d start there. Peppers would be nice, too.
I’d get a fine barn cat, too, to legitimize the whole operation.
