when we trained dd, which was around 2.5, we stuck to nappies for naps for a good while, a couple of weeks, until she was reliably dry on waking up. also used them for excursions for first few days, unless it was v local and she'd just done a wee before we set off.
so after the first few days, when she'd 'got' it, she'd have a wee at the kerbs/at park entrances etc if ncessessary. no portable potty (and no loo seat attachment, couldn't find one to fit and then realised it wasn't going to be that useful anyway).
people were always understanding -- leastways, no one actually confronted us about it.
the first few days we stuck her on the potty the whole time. every half hour or so and always after a meal. were just brisk and 'time to sit on the potty now'. she watched loads of cbbs and got read plenty of stories, so it was all 'fun'. also sticker charts worked great (1 star for a wee, 2 for a no2) -- get her to choose the stickers herself. good book by tony ross, I want my potty.
we talked it up loads with visitors/gparents on phone, what a big girl she was etc. she loved it.
we kept her in knickers from the start, don't think we did knickerless. she loved them too much anyway (ooh, you should let dd choose them, she'll love that)
get loads of potties so you've got them all over the place, one in sitting room, one in loo etc.
she was ready for it, and it was much easier than i'd expected
hope it goes ok.