At the Thai Wat that I frequent there is a ceremonial giving of robes, which is highly organised (the robes are flown in from Thailand). Some of the "prominent" lay people do the actual presentation. The other lay people (such as me!) bring other requisites. I would suggest talking to the lay people at Ven Rahula's monastery, or Ven Rahula himself, to find out when they will hold Kathina (for Thai monastaries it's not a fixed day, it's just sometime during the month after the end of the rains retreat, I presume it's the same for Sri Lankan monasteries), and what their particular organisational procedure is, what sort of stuff is useful, and so on.