Shelter: Get a van. Live in it. Boondocking is better than the cardboard box or couch surfing.
Food: Noodles. Vegetables. Rice. Chicken.
Tech: android tablets can run Linux and can support mouse and keyboard. Tablets are easier than laptops to charge. Laptops can do more. Trade offs.
Security: get some money into bank account ASAP. Make it a regular habit. Any money you’d put into alcohol etc put it into bank account. This is your safety net. Start from zero.
Street address: get a mailing address. Parents/friends may be able to help. You only need to visit. post office box can help as well but costs money.
Relationships: be careful. Your safety net is likely not strong enough to tolerate much failure. Counter argument: having someone else around can help in little ways.
Decisions: think critically. Need versus Want.
Mental health: read autobiographies. Read fiction. Read. Improve all gaps that seem easy to fix. Understand that homelessness is a hole you can dig yourself out of.
Health: teeth, hair etc hygiene is king. Drop any kind of drug other than coffee. Alcohol etc will make you an easy target.