We have done DLR many times in the rain. Waterproof/water resistant shoes are nice, bring an extra pair or two of shoes and multiple pairs of synthetic socks (ex smartwool). I prefer an athletic rain jacket with arm pit ventilation and a hood vs a poncho/umbrella. Some water resistant pants are also nice. If you have a reasonably short walk to your hotel, an occasional break to dry out and change clothes is a game changer. Watch out for puddles, DLR is notorious for poor drainage. Most of the time rain = blissfully short wait times.