Where are you staying OP? I know the area well. 
Go ape glentress is excellent, superb zip lines. Good biking as well if into that.
Other direction, kimmerston stables good and do beach rides.
Ryze near Edinburgh trampoline indoor place.
Festival on in Edinburgh. Train from tweed bank, fifty minutes right into centre loads to do.
Alnwick castle and gardens is fab.
Schools go back next week so lots winding down locally. There is a what's on guide you will be able to get in tourist info.
Food wise in Kelso itself? Cobbles nice, contended vine lovely. Lemon and thyme new but heard good reports. Lunch time cafe u excellent.
If you venture to Alnwick, Milan in wooler worth a stop on way home.
If you give me more info on likes etc I can point you in right direction.