Trains are fairly expensive without a 40% reduction card. A reduction card holder (which includes every student) can take up to 3 other people with the same reduction. Ask young people on the platform if they're students and would be willing to take you.
If you hold a train ticket to Belgium you can take the high speed Fyra train between Amsterdam, Rotterdam and Breda without the extra surcharge.
In Belgium you can use the Rail Pass (which you can only buy at a station in Belgium), which costs 76 euros for 10 rides. (See the Belgium article for more details.)
Pretty much all Intercity trains in the Netherlands have free wifi now, although very slow.
In general very easy in the Netherlands, on highways as well as on the regional roads. See Hitchwiki.
Hotels are expensive. Check hospitality exchange.
Politics have tried to diminish the possibilities for squatting, but it's still quite a good option in the Netherlands. See Squat.net for more information. Before squatting yourself it's good to connect with more experienced people.
Anti-kraak (anti-squat) can also be an option for a longer term stay in the Netherlands. It's probably hard to get into it if you don't speak Dutch and you don't have references. Be careful though, laws here give you very few rights. Read into the situation to make sure you understand them.
Bewelcome link http://www.bewelcome.org/places/Netherlands/NL
The Netherlands are one of the rare countries where you can find a cheap pot of 'Peanut Butter' (pindakaas), which is a nutritious item that you can easily carry in your backpack. Also, you can find a tube of 'mayonnaise' and 'ketchup' sauce (Zaanse saus) for about 30 cents, which last long without needing to be refrigerated and are great supplements to sandwiches or friet (as it avoids having to pay the 50 cents sauce at the snackbar (or sometimes frituur or frietkot, especially in Belgium) when ordering a snack).
Food in restaurants is generally expensive, supermarkets offer a better deal.
Dumpster diving is very possible in cities.
Prepaid mobile: Bliep offers unlimited internet for 50 cent per day, or 10 MB of roaming data in the EU for 2 euro per day, or 100MB in a week for 15 euro.