No garden, no roof access, and a landlord. Many solutions within this catalogue assume a house; these are some of the options that do not and will also work in an urban flat.
Bokashi fermentation composting: Anaerobic fermentation in a sealed bin; handles cooked food/meat scraps that open composting struggles with. — Why this one: Odourless, sealed, and sized for a kitchen cupboard. Will handle your waste efficiently
Haybox / retained-heat cooker (fireless cooker): A heavily insulated box that a pot is put into after being brought to the boil. The heat already in the pot keeps it simmering for hours with no more fuel, and — Why this one: Needs a hob for ten minutes and nothing else. Cooking continues with no additional energy afterwards
DIY activated-charcoal air filter: A bottle or box filled with activated charcoal, left in a room without a fan. Charcoal traps some fine dust and chemical vapours from the air passing it. It is — Why this one: Healthier interior air after just an hour's work.
Insulated draft-blocking curtains: Homemade curtains with an outer fabric and an inner reflective or insulating layer, sealed to the window frame with Velcro. They stop cold draughts and keep the — Why this one: An easy way to stay warmer in winter, and to save money on energy bills.
This is a short list, not the whole catalogue
All the solutions for your home are in the catalogue, organized by need.