What to buy?
Gundel set of cheese
Aged in gundel wines or with walnut pieces or seasonings. most easily found in 350g sets of three kinds in duty-free of ferihegy airport in budapest at least in terminal 2, but is likely available in gundel 1894 food & wine cellar see pest#eat. keep in mind that shelf life for this cheese is only 2 months.
The unit of Hungarian currency is known as the forint HUF. The Hungarian "cent" fillér is long since obsolete.
Bank notes come in denominations of HUF20,000, 10,000, 5,000, 2,000, 1,000 and HUF500, coins are HUF200 two coloured, similar to a one euro coin, HUF100 two coloured, similar to €2, HUF50, HUF20, HUF10 and HUF5.
Euros are now accepted at most hotels and some of the restaurants and shops. Make sure you check the exchange rate though, sometimes even well known places like McDonald's will exchange at unrealistic rates.
You can use major credit cards EuroCard, Visa in major shops and larger restaurants, but never expect that without checking first. Small places cannot afford to handle cards. ATMs are available even in small cities, the coverage is good.
While completing any monetary transactions, it's best to pay in forint when you can. Some restaurants and hotels charge a steep rate for euro exchange and often, due to the fluctuation in exchange rates, cost and services stated may vary drastically.
There were 285 forints to the US dollar and 300 forints to the euro in March 2015. Shopping in Hungary is extremely cheap for people from the US and the euro zone.
Exchange rates for EUR and USD are roughly the same downtown at least in Budapest and Eger. Rates will likely be much worse in airports and large train stations - so change exactly what you need to reach downtown. A good habit is to compare the buy and sell rates: if they are drastically different, you're best going somewhere else. Official exchange offices always give a receipt and normally have a large glass between client and a cashier making all steps transparent for client.
Travellers report that unofficial money changers operating nearby an official money changing booth offer unfavourable rates--and recommend to use official exchange offices. It's worth noting that such exchanges are illegal. If someone offers to change at a very good rate, it is to actually slip you less money with some hand trickery, hoping that you won't notice till later.
If you arrive to Budapest at late nights or state holidays it is quite likely you won't be able to find any working bank or exchange office. In this case you may attempt to exchange your money with any random taxi driver. They will rip you off by HUF100-200 around €1, but it's better than nothing. There is an ATM in the arrival hall at Budapest Ferihegy, and the rates for using ATMs with a card are often better than the bureau de change. There are many banks machines in Budapest which will accept European and North American debit/credit cards, if it becomes necessary, it maybe in your best interest to draw a sufficient amount for your stay and it will often give a more much favourable rate.