This one is easy but can be very hit and miss. Hostels that have a kitchen will usually have a 'Free Food' shelf or box. Basically when people leave the hostel they often don't have room or can't be bothered to take all their food with them and so leave it on the free food shelf. This food is then up for grabs to the fist person who comes along.
The staple contents of free food shelves are pretty much universal and you will usually find a few packets of 2 minute noodles (the backpackers staple), half a loaf of bread, half a jar of jam/peanut butter/vegemite, salt & pepper, packets of McDonald's ketchup, and some teabags. Quite often you will also find a few potatoes and some sundry fruit and veg. It's up to you how much of meal you can make of it.
Local library's always have free internet, sometimes you must prove local residence though. However if you are ever in Brisbane the State Library of Queensland on the South Bank will let you sign in as a guest for 1 free hour of internet 'research'. Also in Australia look out for flyers advertising the Peterpan travel agency which usually have a voucher attached for 20 mins free internet access.
free entertainment is usually easy to comeby if you are in a big city, epecialy if you can master the knack of sitting on a single glass of coke for 2 hours. Loads of Pubs & bars have free entertainment ranging from bands and comedians to pub quizzes where you can win yourself some much needed cash. Also look out for flyers and adverts in local papers for all sorts of free stuff from concerts and gigs to free film screenings, art gallery open evenings, free museums, arts and crafts work shops & loacl guided walks. With the minimum of effort finding free stuff to do is pretty easy.
Most hostels have a 'Library' or book self with books which are free for you to take. The idea being that you replace it with a book of your own that you no longer want.
Sometimes the books available are complete crap. At the moment 90% of the books available in my hostel are foreign language due to the high turn over of English language students staying there but occasionaly a gem will turn up like the copy of Northern Lights by Philip Pullman I snagged last week.
Freen accomodation is much harder to come by, but most backpacker hostels will offer some limited work for accommodation. Usually this involves a 3 hour shift of house keeping/cleaning/bar work/handing out leaflets each day in exchange for a free nights accommodation.
These jobs are very much in demand and you have to be quick to snap them up when the opportunity arises. Sometimes they will want you to agree to work for a minimum amount of time as they don't like having to train you up and then loose you after a few days. But there's no harm in saying "yes I'll be here for 2 months" and then quitting after a week. It's a bit dishonest but hey you're broke and they won't have any problems finding someone else to take your place.
Sometimes you'll even get free meals and some cash in hand thrown in but this all depends on the hostel and how tightfisted they are. Bar work and work in the kitchens is always good because even if its not officially part of the deal a nice bar manager or friendly chef will bung you a few free drinks or meals 'cos they like you and they know what it's like to be a broke backpacker too.
Work for accom is also available a some pubs and hotels too. So if you can't get any at the hostles in town try the Hotels and Pubs (not bars) you're also more likely to get meals and money thrown in as well.
Being a Mothers helper or au pair is always a good way to get money and accom if you don't have any child acre qualifications but you are usually expected to do a lot more work for less pay and you may have some really bratty kids to look after. But the advantage to this is you get to experience life with a local family, usually out of the usual tourist and backpacker haunts and submerse yourself in local life (and you quite often get the use of a car).
Finaly there is alwayd the option of pulling a local and spending the night at their place. You might even get breakfast out of them !
Other free stuff
Tampons & Condoms
We all know these are a necessity, and often quite expensive. But if you know where to look it's not actually that hard to score yourself a free supply of sanitary products and free condoms.
You will often find that in your posher hotels (especially in the USA) there is a free supply of sanitary products in the ladies wash rooms. Often you wont notice but sometimes the tampon dispensing machines will say complementary. and when you twist the knob or pull the handle out popsm a free tampon all packaged up nicely ready for you to pop into your hand bag. And you can keep popping them out until you have all you need or someone walks in and you have to stop because you don't want them to see what you are doing (these machines usually dispense free condoms as well). Some times in the very best hotels there won't be a machine as they would spoil the look of the carefully designed room but if you look carefully you can usually find a stash hidden away in an ornamental box or drawer in an otherwise useless design feature.