I think it depends on what game packs/expansions you have too. IMHO, City Living makes it easier to be homeless. There is a produce vendor that spawns fairly regularly in the area that hosts the Spice/Flea Markets. The Spice Market also spawns with at least 12 plants. This is in addition to all the plants mentioned above. Due to weddings/parties needing cooking facilities, some places have stoves in addition to the grills in the parks. So you can get better food. The City Living main park is set up this way, and the new art venue has easels and workbench as stock items. City Living also has all the food stalls, some open through the night. So with even a little money you can also buy food. Lounges have instruments, as always, but City Living adds busking stands to help you use that for money once you buy an instrument.
Also, if you have the Outdoors one, the cooler and tent can be bought and both have a "Place in Inventory" action where the sim can carry their own tent and cooler and then pitch them (Place in World) in the parks for sleep/eating and then put them back in inventory. The cooler doubles as a seat. If you start on a lot, the bush that doubles as a bathroom works well too, it is not an inventory item. Though if you use the parks of course you don't need the bush.
The Get to Work active careers also provide some facilities, so you can make a salary while getting some food and having (depends on job) some workout, computer, food and some benches for sleeping. That may sound cheesy, but I know more than one person who took a job out of college into an area that was pricey to live in that lived out of office/car/cafes until they saved enough or got to the top of a wait list.
So whether you start out with the empty lot and no money, or have rules forcing you not to use a lot until "you meet X goal(s)" .. I think the additions allow you to better mimic homelessness of several types. You can collect for quick food sales, while using public facilities. You can start collecting items to provide shelter/needs early while remaining mobile and still needing public facilities. You can also, if you have Outdoors, slowly set up a rough homeless camp that looks like one (cardboard dance floor is an interesting decoration and useful for fun), a tent and a bush on a lot as you progress. If you find a way of getting elderberry, it is the only one of the three ingredients for the Outdoors hygiene potion that you can only get from a vacation. It doesn't require an insect, so if you do use a lot that brings it in, or go there for a day to get some, you can grow the three needed ingredients in pots and keep making it.
I understand some of the rules with regards to selling gathered items in the game since some are very generous. Fishing seems quite useful in Sims 4 for sale as well as food. So depending on how tight you set those rules, and what expansions you have and allow, I think it may be easier.