there are lots of useful tips on various websites (google panic attack tips) which work for most people.
Some which are tried and tested in our group include: telling yourself: ''this will pass, this cannot hurt me''
Do some 'yogic' breathing - breathe in deeply to count of 3, hold for count of three, exhale deeply to a count of 3, repeat
Splashing your face with cold water
Singing out loud
Talking to a friend (NOT about the panic you are feeling)
Take regular exercise (even walking)- this helps to burn off excessive adrenaline.
Avoid cigarettes and alcohol. Eat regular meals and avoid processed foods and drinks, to keep blood sugar levels stable.
Keep moving - don't sit down or 'give in' to the symptoms.
Try and avoid stressfull situations or things likely to trigger an attack for a while (eg, if the supermarket is nightmarishly busy on a Friday morning, go on a thurs eve instead)
I know some of these seem easier said than done, but pervsevere, you will find something which works for you.