Do you have any charity shops with furniture sections nearby? I got lots of my stuff from one of those when I moved into my house a few years ago. My sofa was £30! It was a bit tatty but very comfy - I chucked a throw over it and only got rid of it earlier this year when I treated myself to a new one (Ikea, nothing pricey). They often deliver too (for a small fee).
Somewhere to sit and eat meals is useful, if you have space - folding tables and folding chairs are a godsend if you don't have much room. Again, easy to come by second hand.
I bought a brand new fridge-freezer rather than second hand, but I think everything else was either given to me or I bought from the chazzer.
Some friends gave me their old spare bed and mattress, which I replaced with new earlier this year once I could afford it.
Otherwise, basics you might need are:
• bath mats (get two so you can use one and wash one), towels etc
• loo brush, as above
• cutlery (I'd buy new), plates, mugs etc (plenty in charity shops for cheaps, or try eBay)
• pots and pans
• ironing board and iron (if you can be arsed!)
• clothes airer
Gumtree has a freebie section that's worth a look, as well as their for sale section. I've also bought off eBay. Your workplace (if you're working) may have a noticeboard with things for sale, or an intranet page. Try your local community facebook page - mine has loads for sale/freebies but you need to be quick!