The border with Spain is open 24 hours a day, and you can drive or walk in with no restriction on the number of border crossings in a day. Fraudsters may attempt to charge you for a 'ticket' to enter Gibraltar, just ignore them and report it to the Spanish Police. The legal tender in Gibraltar is Sterling. The Gibraltar Government issues notes and coinage. UK notes and coins are equally welcome.
Many places accept other international currency.
There is no restriction as to how much currency you can bring into Gibraltar. There are a full range of international banks, including several UK institutions. Banks are generally open from 9 am. Credit cards and travellers cheques are widely accepted. All EC nationals can enter Gibraltar with identity cards or passport.